The Occurrence of Intercalary and Uninterrupted Meristems in the

The Occurrence of Intercalary and Uninterrupted Meristems in the Internodes of Tropical
Monocotyledons
Author(s): Jack B. Fisher and James C. French
Source: American Journal of Botany, Vol. 63, No. 5 (May - Jun., 1976), pp. 510-525
Published by: Botanical Society of America
Stable URL: http://www.jstor.org/stable/2441815 .
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Amer. J. Bot. 63(5):
510-525.
1976.
THE OCCURRENCE OF INTERCALARY AND UNINTERRUPTED
MERISTEMS IN THE INTERNODES OF TROPICAL MONOCOTYLEDONS'
JACK B. FISHER AND JAMES C. FRENCH
FairchildTropical Garden,Miami,Florida 33156
A B S T R A C T
The distribution
of percentof dividingnuclei,parenchymacell length,totalcell numberper
internode,and total internodelengthwere determined
for successiveinternodesin the apex
and growingvegetativeinternodesof 23 tropicalspecies in 17 familiesof monocotyledons.
Basal intercalary
meristems
(IM) werefoundin representatives
of Commelinaceae,Cyperaceae,
Flagellariaceae,Poaceae, Restionaceae,and Marantaceae. Uninterrupted
meristems(UM)
whichare confinedprogressively
to theupperregionof theinternode
and are notisolatedmeristematicregionswerefoundin theCostaceae,Dioscoreaceae,Philesiaceae,Smilacaceae,Agavaceae, Araceae,Arecaceae,Liliaceae, Pandanaceae,and Zingiberaceae.Both IM and UM were
foundin different
speciesof Orchidaceae.The onlymorphological
traitcorrelatedwithmeristemtypewas presenceof sheathingleaf bases in all specieswithIM. Both IM and UM are
as extensionsof theprimaryelongatingmeristem;the IM is disjunct,and the UM
interpreted
is continuous
withit. The phytomer
growthunitand thepresenceof internodal
IM's cannotbe
appliedgenerally
to themonocotyledons.
PRESENCE of localized regions of meristeMATERIALS AND METHODS-In
order to limit
meristems(IM)2, at the the numberof species used in this survey,only
maticactivity,
intercalary
base of internodesis oftencitedby botanistsas a thosewithrelatively
longinternodesin theiraerial,
generalfeatureof monocotyledons.Internodalin- vegetativeaxes were selected. Rhizomes and intercalarymeristemsare widespread in grasses, florescenceswere not examined. Thus, several
Poaceae, and occur in the Cyperaceae and Com- predominantly
herbaceous(e.g., Xyridaceae,Eriomelinaceae (see referencesin Discussion). How- caulaceae) and aquatic familieswere eliminated
about fromthis study. In addition,species in whichinever,thereis a lack ofpublishedinformation
internodedevelopmentin the other groups of ternodeelongationonly occurs withinthe inflomonocotyledons,
mostofwhichare predominantly rescence (e.g., Typha, Musa) were not studied.
tropical. Tomlinson(1970) has pointedout that In those species with determinateshoot growth
the common and oftenerroneousgeneralizations due to terminalflowering(e.g., Alpinia, Costus,
of the monocotyledons
are based on economically Scleria) or sympodialgrowth(e.g., Philodendron,
temperatespecies of Freycinetia,Cordyline) the early stages of shoot
importantand predominantly
initiationwerechosen
the Poaceae. In answerto his plea for more re- growthbeforeinflorescence
for
examination.
and in orderto
search on tropicalrepresentatives
A basic assumptionin our study is that sefurnishneeded data, we have undertakenthe folquentially
developinginternodeswill show qualiin selected
lowingsurveyofinternodedevelopment
tativelythe sequential ontogeneticpatternsof a
tropical monocotyledons. We will attemptto singleinternode.Althoughthereare oftenquandemonstratethe location of regions of meriste- titativechangesin phyllotaxy
and internodelength
matic activityin developinginternodes,correlate along a shoot axis, all internodesexceptthose at
thesewithmorphologicalcharacters,and examine the extremebase of the shoot or in the apical inthe taxonomicdistribution
of the types of inter- florescencecan be expectedto develop similarly.
nodal meristems.
In indeterminateshoots with axillary inflorescences (e.g., Chamaedorea, Vanda) all interReceivedforpublication31 March 1975.
nodes are alike afterthe juvenileor establishment
The authorsthankDr. P. B. Tomlinsonformaterialof
Korthalsia fromNew Guinea (his collectingsupported phase oftheshoot.
Activelygrowingshoots were collectedin late
and NSF
by theCabot Foundationof HarvardUniversity
Grant GB-5762), Dr. D. R. Kaplan for materialof morningor at midday. Afterolder leaves were
Restio fromthe Universityof California,BerkeleyBo- removed,the apical regionand successivelymore
tanical Garden,Dr. J. Mitchellfor useful suggestions,
and Ms. Jan Wassmerfor carefuland patientmicro- proximaladjacent internodesup to the youngest
technicalassistance.Researchsupportedby NSF Grant matureinternodewere fixed in FAA or CRAF
GB-40065.
Abbreviations
used in text: IM, intercalary
meristem; (Jensen,1962).
In long internodes(> 3-4 cm) only 1-cmsegUM, uninterruptedmeristem;In, internode.
THE
1
2
510
May-June, 1976]
FISHER
AND FRENCH-MERISTEMS
OF TROPICAL
MONOCOTYLEDONS
511
mentsfromthe upper,middle,and lower regions Giffordand Corson (1971) have discussed the
were fixed. The materialwas embeddedin Para- factthatthe mitoticindex does not necessarilyreplast, sectionedlongitudinallyat 10-15 ptm,and flectthe rate of cell divisionsince the durationof
stained with haematoxylin,safranin, and fast mitosis and interphasecan vary independently
in mitoticac- fromeach other.
green. In orderto avoid differences
Drawingsof shootsin Fig. 3-6 weremade with
tivityand cell elongationthatare knownto occur
among various tissues (Fisher, 1970; Evans, a Wild M20 drawingtube. Morphologicalillus1969), onlythe groundparenchymain the center trationsin Fig. 1, 2 are the work of Priscilla
of the axis was measured,except for the more Fawcett.
peripheralparenchymain the hollow internodes
The species examined and their families are
of Restio. All cells were measuredin the apical listedbelow, alphabetically
by genus:
dome and in those younginternodeslackingpro[Zingiberaceae]
cambial strands. Replicate measurementswere Alpinia pur-pulata
(Vieill.) K. Schum.
takenfromthefivemostmedianlongitudinalsections of the apical region. The total internode Chamaedorea seifrizii Burret [Arecaceae = Palmae]
lengthand the numberof cells in a longitudinal Cordyline terminalis Kunth [Agavaceae]
[Costaceae]
file for each internode(delimitedfromone leaf Costus pulverulentus
Presl. (Hybrid?)
axil to the next lower axil) were measured di[Orchidaceae]
rectlywithan ocular micrometer.Cell lengthfor Dendrobium superbum
Reichb. f.
these internodeswas calculated by dividingtotal
[Arecaceae= Palmae]
Desmoncussp. (aff.
internodelengthby total cell number.
D. Schippii Burret)
Numberingof internodesis as follows: Inter[Dioscoreaceae]
node 2 (In2) includes the node of the second Dioscorea alata L.
[Flagellariaceae]
leaf primordium
fromthe apex and the internode Flagellaria indica L.
[Pandanaceae]
above thethirdleaf. Only the upper,middle,and Freycinetia cumingiana
Gaud.
lower (or only upper and lower) regions were
[Liliaceae]
measuredin internodeslongerthan about 5 mm. Gloriosa rothschildiana
O'Brien
In these cases cell lengthwas determinedby the
[Arecaceae= Palmae]
numberof cells per 330,um ocular scale. Total Korthalsiasp.
[Philesiaceae]
numberof cells was also countedin internodesup Luzuriaga latifolia
(R. Br.) Poir.
to 10 mm long. Average internodelength,cell
[Commelinaceae]
number,and cell lengthwerecalculatedfromfive Palisota thyrsifloraBenth.
replicates.
[Araceae]
Philodendron oxycardium
Schott
Mitoticindex (= percentageof nuclei in divi[Restionaceae]
sion) of groundparenchymawas also determined. Restio tetraphyllus Labill.
All nucleiin a fieldof view werecounted,and the Scindapsus aureus
[Araceae]
numberclearlyshowingany stage of mitosisfrom
(Lind. & Andre) Engl.
prophaseto telophase (includingany evidenceof Scleria secans (L.) Urban [Cyperaceae]
the phragmoplast) was noted. The nuclei of Smilax auriculata Walt.
[Smilacaceae]
manyspeciesweresmall or we had problemswith Sobralia hybrid
[Orchidaceae]
to disfixationand stainingwhichmade it difficult
(decoia X leucoxanthe)
tinguishprophaseor telophasewithcertainty.In Stromanthe sanguinea
[Marantaceae]
such cases, only anaphase and metaphasenuclei
Sonder
were noted,thus greatlyloweringthe mitoticin- Thysanolaena maxima
[Poaceae = Gramineae]
dex. However,if thisconservativeprocedurewas
(Roxb.) Kuntze
followed,it was done consistentlyfor the entire Tripogandra grandiflora
[Commelinaceae]
loweredmitoticinshoot,resultingin a uniformly
(Donn. Smith)Woodson
dex for the species. Alternatelongitudinalsec- Vanda hybrid"Miss Joaquin" [Orchidaceae]
tions were examined to avoid duplicate counts,
(teres X hooker-iana)
and approximately1,000 nuclei were countedfor
each internodeor region. Fewer nuclei were
meriRESULTS-Intercalary vs. uninterrupted
counted in the apical dome and in the smallest stems-In the followingdescriptions
two contrastinternodes.Some veryshortinternodeswerecom- ing types of meristematicorganizationare combinedforthesemeasurements
and are so indicated pared. An intercalarymeristem (IM) is a
in the graphs. No distinctionwas made in divi- localized regionof cell divisionoccurringbetween
sion countswithrespectto cell plate orientation. regions of non-dividingand usually mature tisRegions of nodal vascular plexi, if present,were sues. The IM in the internodesof monocotylenotcounted.
dons occurs at the base directlyabove the node,
We use mitoticindexas a meansto qualitatively and tissue maturationis basipetal. An unintersites and not to detectquan- ruptedmeristem(UM) is a regionof cell division
locate meristematic
titativedifferencesin the rate of cell division. that,at an early stage, includesthe entireinter-
[Vol. 63
AMERICAN JOURNAL OF BOTANY
512
Sh
E
G
H
meristems.One or more leaves removedin the paired
Fig. 1. Mature internodesof species withintercalary
of the leaf sheathto the enclosedinternode(s). Scale line represents5
drawingto the right,showingrelationship
cm. A. Stromanthe.B. Thysanolaena.C. Scleria. D. Palisota. E. Sobralia. F. Tripogandra.G. Restio. H. Flagleafbase.
ella)ia. sh,sheathing
to the upper
node, but is confinedprogressively
(distal) regionof the developinginternode.UnliketheIM, however,theUM is neversurrounded
by maturetissues. The IM of Tripogandraand
Thysanolaenaare describedfor comparisonwith
the UM of Korthalsiaand Gloriosa. A summary
of the habit,morphology,and vascular structure
is givenfirstfor each species, followedby a descriptionof the anatomicaldata thatis presented
in thefigures.
graphically
Tripogandra (Fig. iF, 4)-Decumbent herb
withdistichousleaves, branchingoccasional with
leaf base sheathingand
terminalinflorescences,
May-June, 1976]
FISHER
AND FRENCH-MERISTEMS
OF TROPICAL
MONOCOTYLEDONS
513
closed,node distinctwithvascularplexus,vascular oppositeto occasionallyopposite or whorleddisleaf base not
tallybeforebranchingand flowering,
bundlesof internodein ringwithcentralpith.
Data forone shootis presentedin Fig. 4. The sheathing,node indistinctand lacking vascular
cell numberin a longitudinalfile and the length plexus, vascular bundles of internodescattered.
from
In generalthe cell numberin a longitudinalfile
of successiveinternodesincreaseconsistently
the second internode(In2) onward. Cell length and thelengthof successivelyolder internodesinincreases slightlyin Inl-5. There is a striking crease. The declinein lengthand cell numberin
increasein cell lengthin theupperand midregions In2 and In3/4 is apparentlydue to variationsin
of In6 and In7, with much smaller cells in the phyllotaxissince leaves 3 and 4 are subopposite.
basal regionsof In6 and In7. The meristematic The average cell length,however,does not show
regionextendsfromthe apex,to upper In7 witha this decrease as would be expected since the
separate but distinctmeristematicregion in the shorterinternodesof a plant are often due to
base of In7. The mitoticindexincreasesto a sub- fewer,ratherthan shortercells. Meristematicacapical maximumin the base of In5 with barely tivityextendsfromthe apex to the mid-regionof
perceptiblepercentagesof cell divisionin the up- In13. There is an obvious subapical peak in
per and mid-regionsof In6 and in the upper re- mitoticindex in In9 and InlO, with a relatively
gionof In7. A distinctpeak occursin thebase of uniformdecline in mitoticindex in lower interof mitoticreIn6. Thereis a clear inverserelationshipbetween nodes. This continuousdistribution
cell lengthand mitoticindex. The localized and gions is typicalfor the UM. There is a balance
isolated regionof mitoticactivityat the base of betweencell divisionand cell growthin In7-11 as
the internode(i.e., lower In7) is typicalfor the shownby therelativelyconstantcell lengthduring
IM. The directionof tissue maturationwithin increasein cell numberand internodelength. Cell
one internodeis basipetalin directrelationto de- growthpredominatesin In12 and Inl3 whichare
creasingcell length,i.e., withinIn6-8 the least regionsof decreased percentageof cells in divimaturecells are foundin thebasal IM region,and sion. Only cell growthaccounts for internode
of metaxylemfirstbegins in the growthin the lower part of In13 in which there
the lignification
upperregionofIn8.
is no cell division. The directionof tissuematuration is acropetal in direct relationto increasing
Thysanolaena (Fig. 1B, 6)-Erect reed with cell length,i.e., the tissuesin the lower regionof
leaves distichous,leaf base Inl3 are more maturethan those in the middle
terminalinflorescence,
sheathingand closed, node distinctwithvascular and upperregions.
plexus, characteristicsclerifiedregion approxiKorthalsia (Fig. 2F, 5)-Rattan climbingby
mately1 cm long directlyabove node, vascular means of spines and hooks on alternateleaves,
bundlesofinternodescattered.
flowering terminal (hapaxanthic), leaf base
The cell numberand the lengthof successive sheathingand closed, node distinctexternallybut
internodesincreasefromIn6 onward. The erratic lacking vascular plexus, vascular bundles of incell numbersand lengthsin In2-5 maypossiblybe ternodescattered.
due to the startof lengthvariationswhich occur
colThe specimenexaminedwas unknowingly
in the several internodesbelow the terminalin- lected at an earlystage of inflorescenceinitiation
florescence.Because of the shortnessof lnl, the in which the youngestleaf primordiasubtended
data forit and the apex are combined. However, shortenedterminalinternodes.This complication
the apex did not show histologicalchange indica- accountsfor the decreasinglengthand cell numtive of flowering.Cell lengthincreasesgradually ber of Inl-3. There is an increase in the cell
fromthe apex to In9. There is a decrease in cell numberand lengthof successiveinternodesfrom
lengthin the upperregionsof InlO (the regionof In4 onward. Cell lengthincreases fromIn2 to
the IM) and an increasein the base of InlO (the In9, tendsto decrease somewhatin InlO to Inl4,
futureregionof sclerenchymanoted above). In and is followedby an apparentrise in the lowersuccessiveinternodes(Inl 1, etc.) thelongestcells mostregionof In 14 wheretissuesare almostfully
occupytheupperand verybasal regionsof the in- mature. The regionof cell divisionextendsfrom
ternode,and the shortestcells occur in the region the apex to below the mid-regionof In14. The
just above thebasal sclerenchyma.The regionsof mitoticindex is irregular,
but withouta repeating
fromthe apex to patternof maxima. In general,however,the perdivisionare similarlydistributed
InlO with localized peaks of mitoticactivityin centageofcells dividingis highuntila declinetakes
nl 1-13 isolated betweenregionsof maturetis- place below themid-regionof Inl2. This uninteractivityis
of an IM. The directionof tis- ruptedregionof decliningmeristematic
sue, characteristic
sue maturationwithinan internodeis basipetal characteristicof a UM. The relativelyuniform
afterthe early maturationof the basal scleren- cell lengthin internodesthat are elongatingand
meristematic
(i.e., nl 1-14) indicatesa close balchyma.
ance betweencell divisionand cell growth.Data
to determine
Gloriosa (Fig. 2N, 3)-Climber with leaf tip was not availableforolderinternodes
tendrils,leaves alternatenear base becomingsub- whethercell elongationpredominatesin the final
514
[Vol. 6 3
AMERICAN JOURNAL OF BOTANY
Lf
,11~~~~~~
IN
QN
Lf
**I'?
J~~~~~~~~~~~~~~~~~J
V.I
meristems.One or more leaves removedin the paired
of specieswithuninterrupted
Fig. 2. Matureinternodes
of the leaf to the enclosedinternode(s). Scale line'
drawingto the rightif theyare sheathing,
showingrelationship
5 cm. A. Philodendr-on. B. Scindapsus. C. Alipinia. D. Luzur-iaga. B. Chamaedor-ea. F. Kor-thalsia. G.
represents
Costus. H. Dioscor-ea. 1. Fr-eycinetia.J. Smilax. K. Vanda. L. Cor-dyline.M. Dendr-obium. N. Glor-iosa. 0. Desleafbase.
moncus. Lf, base of leaf; br, lateralbranch;sh, sheathing
May-June, 1976]
FISHER
AND FRENCH-MERISTEMS
6
8
1
~~~36A
00
2
2~
OF TROPICAL
41L
610z126
>~\~'
A
o~~~~~~~~~~~~8
12
515
MONOCOTYLEDONS
2
160
920
I-~~~~~~~~~~~10
W18012
(D~~~~~~~~~~~~~~~(
z
~
~ ~
020
~
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II~~~~~~~~~10
~
~
8
~~~~~5-
405-
CA-13 020.
0
50
mO
(9
NO.
z~~~~
o~~~~
z
0
LI
H
z
8
~~.0 A
A
Z
7
0.1
0.1
14
14
H
~234 6
8 10
INTERNODE.
13
12
NO.
.0511
A
1
2 4
6
INTERNODE
8
NO.
in
Fig. 3, 4. Comparisonof mitoticindex,cell length,cell number,and internodelengthvs. intemodenumiber
a growingvegetativeshoot of two species. 3. Glo,riosa,withinternodaluninterrupted
meristems.4. Tripogand
ra,
withinternodalintercalary
meristems.A, apical dome. Shaded areas, regionsof cell division.
stagesof internodegrowthas in Gloriosa (Fig. 3). of the oldest meristematicinternode;and (2)
The directionof tissue maturationis acropetal acropetalmaturationin the older internodes.
withinan internode.
In summary,
thebasic featuresoftheabove two
meristems-Only
Otherspecies withintercalary
examples of IM are: (1) isolated meristematic the mitoticindex and cell lengthdata will be preregionsthatare disjunctfromthelargersubapical sentedbelow,althoughcompletedata on cell nummeristematicregion; and (2) basipetal matura- ber and internodelengthwere also collectedand
tion in the internodes,althoughearlyhistogenesis examinedforeach species.
may not followthispatternof finaltissuematuration. The basic featuresof the above two examRestio (Fig. 1G, 7)-Erect herb with interples of UM are: (1) an uninterrupted
meriste- nodes as the main photosynthetic
organs, scale
maticregionfromthesubapexto theupperregion leaves distichous,floweringaxillaryand terminal,
516
AMERICAN JOURNALOF BOTANY
_2
3
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-
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with~~
leaf base sheathingand open, node distinctwith
vascular plexus, vascular bundles of internodein
ringwithhollowpith.
Due to theirshortness,Inl-2 and In3-4 are
combined. Cell length remains rather uniform
fromlnl to In13. From In14 onward thereis a
repeatingpatternof long cells in the upper regions (fullymaturein Inl5) and short cells in
the basal regions. The regionof divisionextends
to In14 in whichthe basal peak in mitoticindex
is relatedto the earliesthistologicallocalizationof
the IM. Active IM's are presentin the bases of
Inl5-17. A centralpithwas stillintactin upper
Inl7.
Sobralia (Fig. 1E, 8)-Terrestrial erect herb
with terminalflowering,leaves distichous,leaf
base sheathingand closed,node distinctexternally
but lackingvascular plexus, vascular bundles of
internodescattered.
Cell lengthis uniformfrom'the apex to In5.
Maximumand minimumcell lengthoccur respec-
May-June, 1976]
n23
_
FISHER
AND FRENCH-MERISTEMS
OF TROPICAL
MONOCOTYLEDONS
8
7-3
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-7INTERNOGE NUMBER
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INTERNODE NUMBER
IO I
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-7
INTERNODE NUMBER
Fig. 7-12. Mitoticindexand cell lengthvs. internodenumberin specieswithintercalary
meristems.7. Restio.
8. Sobralia. 9. Flagellaria. 10. Scieria. 11. Palisota. 12. Stromanthe.A, apical dome.
tivelyin the upper and basal regionsof In6-7.
The firstcompletelymaturetissue occurs in the
upper and mid-regionsof In7. Mitoticindex increases untilIn5. In the firstelongatedinternode
(In6) onlythebase is meristematic,
and it is also
the only IM presentin this shoot. The cells in
base of In7 are immatureand elongating,but are
no longermeristematic.
The youngestcongested internodesare combined into three groups: Inl-4, In5-6, In7-8.
Cell lengthis constantup to In13. Elongationof
cells occursin theupperregionsof In14 and In15.
Cell divisionoccurs from,the apex to Inl 3. The
localized regionof meristematic
activityin In14 is
theonlyactiveIM in thisshoot. The base of Inl5
is immature,but not meristematic.
Flagellaria (Fig. 1H, 9)-Scandent or climbing
Scleria (Fig. 1C, 10)-Scandent climbingherb,
herb with leaf-tip tendrils,floweringterminal, floweringterminal,leaves alternate,leaf base
leaves distichous,leaf base sheathingand closed, sheathingand open, node distinctwith vascular
node distinctwithvascular plexus, vascular bun- plexus, vascular bundles of internodescattered.
dles ofinternodescattered.
Cell length is relativelyuniformup to In5.
518
AMERICAN JOURNAL OF BOTANY
Elongated and completelymaturecells occur in
the upper and mid-regionsof In6 and In7. The
regionof cell divisionis continuousfromapex to
regionin the base of In6
In5. The meristematic
is theonlyIM in thisshoot.
Palisota (Fig. ID, 11)-Erect herb, leaves
in groups of four with an elonspiro-distichous
gated internode separating these pseudo-leaf
leafbase sheathingand
terminal,
whorls,flowering
closed, node distinctwithvascular plexus,vascular bundlesof internodescattered.
Cell lengthfor Inl-4 is combined. Both cell
lengthand mitoticindex data are related to the
distinctivephyllotaxisof this species. Starting
fromthe oldest region,In12 is above one leaf
group,In7 is above anothergroup,and presumably In2 is above the youngestgroup. An IM is
at the base of In12 in whichthe upper and midregionsare mature. A meristematicpeak (presumablythe futureIM) occurs in In7 which is
already noticeablyelongated. Within the short
internodesof a leaf group (In8-11) there is a
basipetal reductionof cell division but no loactivity(e.g., no divisionin
calized meristematic
lnll).
Stromanthe(Fig. 1A, 12)-Erect herbwith45 basal, distichousleaves subtendinga veryelongated internodetopped by a crown of distichous
terminal,leafbase sheathingand
leaves, flowering
but lackingvascular
open, node distinctexternally
plexus, vascular bundles of internodescattered.
Cell lengthincreasesup to In5, the lowest internodeof the growingleaf crown. The actively
growing,elongatedinternode(In6) has long and
fullymaturecells above thelowerregionsof short
cells. Cell divisionoccurs fromthe apex to In4.
There is an activeIM at the base of In6.
[Vol. 6 3
Alpinia (Fig. 2C, 14)-Erect herb, flowering
terminal,leaves distichous,leaf base sheathing
and open, node distinctbut lacking vascular
plexus, vascular bundles of internodescattered.
Cell lengthincreasesfromthe apex to In4, then
declines in In5 and In6, and finallyincreasesin
In7-9. Mitoticindex reaches a maximumin In6
and declines irregularlyto the upper region of
In8. There is less of a balance betweencell division and cell elongationbecause cell lengthincreases in those regionswith low mitoticindex
(e.g., peak in In4).
Dioscorea (Fig. 2H, 15)-Twining vine with
alternate leaves, floweringaxillary, leaf base
externally
(petiole) not sheathing,node indistinct
but withvascular plexus,vascular bundles of internodescattered.
Cell lengthincreasesfromthe apex to In6 and
thenremainsrelativelyconstantuntilit increases
in In12 and Inl3. Mitoticindex fluctuatessomewhat untilthe mid-regionof Inl afterwhich it
decreasesto zero in thelower regionof InI2.
Desmoncus (Fig. 20, 16) -Rattan climbingby
means of spines and hooks on alternateleaves,
flowering
axillary(pleonanthic),leafbase sheathing and closed, node distinctbut lackingvascular
plexus,vascularbundlesof internodescattered.
Cell lengthis constantfromapex to 1n6, and
thenincreasesto a broad peak at InlO withsome
and perhapsa declineuntilthereis an
fluctuations
increase in Ml 3. Mitotic index falls from an
apical high and remainsvery low and constant
untila subapicalpeak is reachedin In12, and then
it decreasesto zero. The peak in cell divisionin
1nl2 is correlatedwitha possible decreasein cell
lengthin In12. There is rapid maturationafter
cessationof cell divisionsince metaxylemsecondin
ary walls show pittingand early lignification
the lower region of MlO3,althoughcell division
occurs in the middle of that same internode.
meristemsOther species with uninterrupted
Only themitoticindex and cell lengthdata willbe
presentedbelow, althoughcompletedata on cell
numberand internodelengthwere also collected
Dendrobium (Fig. 2M, 17)-Epiphyte climband examinedforeach species.
ing by roots,floweringaxillary,leaves distichous,
leaf bases sheathingand closed, node distinctbut
Luzuriaga (Fig. 2D, 13)-Twining vine with lacking vascular plexus, vascular bundles of inscale leaves on the primaryaxis studied here, ternodescattered.
Cell lengthincreasesfromthe apex towardthe
lateral branches leafy, scale leaves distichous,
floweringaxillary,leaf base not sheathing,node base with slightdecreases in 1n3 and lower 1n7.
indistinctand lacking vascular plexus, although Mitoticindex decreasesin lnl and 1n2, peaks in
developingaxillarybuds later develop manyvas- In3, followedby a basipetal decline to zero in
cular connectionsat the node, vascular bundles lower1n6.
ofinternodescattered.
Cordyline(Fig. 2L, 18)-Erect woody shrub,
Data forapex and the veryshortlnl are combined. Cell lengthincreasesslightlyfromapex to floweringterminal,leaves alternate,leaf base
In12 and thenrapidlyincreasesin Inl 3 and In14. sheathingand open, nodes distinctbut lacking
Mitoticindex peaks in the upper regionof InlO vascular plexus, vascular bundles of internode
and then declines. Cell divisionand cell elonga- scattered.
The apex is sunkenbelow the raised regionof
tion are almostbalanced untilthe upperregionof
Inl3, at whichlevel mitosisstops and cells elon- leaf insertionsof the firstfiveleaf primordia.In
this region of primarythickeningthe leaves are
gategreatly.
May-June, 1976]
FISHER
FRENCH-MERISTEMS
AND
13--2
4
4tL
z
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o A-1 4 6 8- 10
--L'12'
2-4'
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-
20
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INTERNODE
6
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NUMBER
_
_
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A 2 4 6 8
_
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'12'
6
1
3I
1
18 3
1
-
120-
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MONOCOTYLEDONS
14-
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TROPICAL
-
L -2
O
OF
I
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2
0A
-
Q,I
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8'-8-----
INTERNODE
'
NUMBER
1:
3 7 1'
4 8 12
14
L
'
_ L
16
20-
A 3 7 11
-
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' 8
2
4 8 12 14
16
1
INTERNODE NUMBER 0
Fig. 13-19. Mitotic index and cell length vs. internode number in species with uninterruptedmeristems. 13.
Luzuriaga. 14. Alpinia. 15. Dioscorea. 16. Desmoncus. 17. Dendrobium. 18. Cordyline. 19. Freycinetia.
A, apical dome.
all insertedat about the same level so that there
is no measurable longitudinalinternodelength.
Therefore,thefirstfiveinternodescannotbe measured. The firstdistinguishable
internode(In6) is
already1,064 umlong. Cell lengthshows a relativelyuniformincrease. Mitotic index peaks in
the lower regionof In6 and the upper regionof
In7 and thendeclines.
maximumregion(Inl3-15), followedby a basipetal decline.
Costus (Fig. 2G, 20)-Erect herb, flowering
terminal,leaves alternate,leaf base sheathingand
closed, nodes distinctwith vascular plexus, vascular bundles of internodescattered.
In17, 18, and 20 were skippedin samplingbecause of themassivesize of the subapical growing
Freycinetia(Fig. 21, 19)-Erect woody shrub, regionof thislarge herb. Cell lengthincreasesto
floweringterminal,leaves alternate, leaf base a peak in In8, then decreases to a minimumin
sheathingand open, nodes distinctbut lacking In15, followedby a strikingincrease. In older
vascular plexus, vascular bundles of internode internodes(In19, 21) the mid-regionhas shorter
scattered.
cells than eitherthe upper or lower regions. The
Data for congested internodes(Inl-12) are mitoticindex decreases fromthe apex to a minigrouped in pairs. Cell lengthremainsrelatively mum in In9, rises to a fluctuating
peak in Inl2constantwith a slightdecrease in Inl3-15, and Inl6, and then declines with no cell divisionin
thenthereis a gradualincreasefromIn15 basip- In21. The declinein lower Inl5 may not be sigetally. Mitoticindex decreases fromthe apex to nificantsince it does not follow a pattern. The
a mninimum
in In7-8, then rises to a fluctuating apparentlack of cell division in the mid-region
3
22
z
020
~-
I
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-5
E10>1~A 1-4 5-7
120
22,
14
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,,,,,
Z
-
~~~~~~~~~~~~~~~~~60~~~~~~~~~~~~~~~~~~40-
40
20
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2
200
o il
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6 8 10
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[Vol. 63
AMERICAN JOURNAL OF BOTANY
520
O+
INEND
ASA 24
2
6
4
34
NUBRINENDENME
4 --
_____________
V4
-I
~~~~~~~20-
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _I
PA+1
23 67
-1O-----l2
INEND
`1 4'
UBRINTERNODE
A SA
I
NUMBER
20-
2
1
1
`A
I
I
INTERNODE
2TE4NOD
NUMBER
-- - - -- -
NUMBE
meristems.20.
Fig. 20-25. Mitoticindexand cell lengthvs. internodenumberin species with uninterrupted
21. Scindapsus. 22. Vanda. 23. Smilax. 24. Philodendron. 25. Chamaedorea. A, apical dome; SA,
subapicalregionabove firstleaf.
Costus.
althoughthisis uncerof In19 maybe significant,
tain due to the low mitoticcountsinvolved. The
decreased cell lengthin the mid-regionof In19
would indicatethatthe apparentisolated mitosisfreeregionof In19 is an artifactsince an increase
in cell lengthwould otherwisebe expected. Therefore,this species is interpretedas not possessing
a definedIM, althoughit may representa formof
betweenthe
UM whichis somewhatintermediate
twotypes.
in In4, rises to a maximumin In5, and thendeclines.
Vanda (Fig. 2K, 22)-Erect herb or epiphyte
climbingby roots,floweringaxillary,leaves terete
and alternate,leafbase sheathingand closed,node
distinctbut lackingvascularplexus,vascularbundles ofinternodescattered.
Data forthe apex and firstsmall internodeare
combined. Internodeelongationis abrupt with
cell lengthincreasingafter In2. Mitotic activity
Scindapsus (Fig. 2B, 21)-Climber by means extendsto In3 withno dividingcells in upperIn4.
of roots,floweringterminalbut appearinglateral,
Smilax (Fig. 2J, 23)-Climber with stipular
leaves alternate,leaf base sheathingand open,
node distinctbut lackingvascularplexus,vascular tendrils,leaves alternate,floweringaxillary,leaf
base not sheathing,node indistinctexternallybut
bundlesofinternodescattered.
Data forthe apex and the firsttwo shortinter- withvascularplexus whichis onlywell developed
nodes are combined. Cell length remains rela- at nodes withbranches,vascularbundlesof intertively constant and increases in In7 and In8. node scattered.
Mitoticindex decreasesfromapex to a minimum Data for the apex and congested internodes
May-June, 1976]
FISHER
AND FRENCH-MERISTEMS
(Inl-7) are grouped in pairs. Cell length increases slightlyfromthe apex to In8, then remains relativelyconstantuntilit increasesbelow
the mid-regionof In12. Mitoticindex in general
decreasesfroman apical high to zero below the
of In12 with a veryslightamountof
mid-region
mitoticactivityin theupperregionof Inl 3. However,the activityin In13 is so low that it is not
different
fromlower Inl2.
significantly
OF TROPICAL
MONOCOTYLEDONS
521
the isolated meristematicregions have been demeans. Surfacemarkingsdemtectedby different
onstratedbasal regions of prolonged growthin
culmsof Scirpus (Seidel, 1955) and Cyperusand
grasses (Buchholz, 1920). Measurementof cell
lengthwas used to locate the basal regionof inin Triticum(Ordina, 1952).
ternodeimmaturity
Directexaminationof tissuesof sedgesand grasses
located basal regions of immatureand dividing
cells (Evans, 1965; Fisher, 1970; Kaufman,CasPhilodendron(Fig. 2A, 24)-Climber-epiphyte sell and Adams, 1965; Miltenyi,1931; Schmalby means of roots, leaves alternate,flowering, fuss, 1930). However,onlythe firsttwo authors
lateral,leaf base not sheathingbut with a large (Evans, 1965; Fisher, 1970) presentedcomplete
of mitosesin
abscising cataphyll encirclingnode and young quantitativedata on the distribution
leaf, node distinctabove the cataphyllscar but the developinginternodesimilar to the present
withoutvascular plexus, vascular bundles of in- study.
ternodescattered.
Well definedIM's onlyoccurin thelaterstages
There is a distinctlyelongatedsubapical zone of internodaldevelopment. In early stages the
above the firstleaf primodium(SA in Fig. 24) entireinternodeis unifornlymeristematic.The
whichmay be associated withearlyinflorescence size of this regionremainsrelativelyconstantin
initiation. Cell length graduallyincreases from the single elongated internodesof Cyperus and
the apex to lower In4 and thenrapidlyincreases Eleocharis (Fisher, 1970; Evans, 1969) and iniin InS. Mitotic index increases below the apex tiallyincludesthe entireinternode.Afterfurther
decreasein In2. There internodeelongationand maturationof the upper
witha possiblysignificant
is a steadydecrease in mitoticactivityfromupper region,the meristematic
regionis distinguishable
In3 to upperInS.
as an IM. In the finalstages of internodedevelopmentthe basally isolated IM decreases in size
Chamaedorea(Fig. 2E, 25)-Erect woodystem, and activity,
and itselfmatures.Otherspecieswith
leaves alternate,floweringaxillary(pleonanthic), a single elongatedinternodealso show this patleaf base sheathingand closed, node distinctbut ternof development,e.g., Stromanthe(Fig. 12).
lackingvascularplexus,vascularbundlesof inter- The same sequence of an initiallyuniforminternode scattered.
nodal meristemfollowedby basipetal maturation
Cell lengthremainsconstantfromthe apex to witha resultingisolatedIM at thebase is foundin
In3 and thenincreasesbasipetallyfromIn4. The species withan IM in everydevelopinginternode,
decrease in cell lengthin upper In7, whichis al- e.g., Tripogandra (Fig. 4), Restio (Fig. 7),
most fullymature,appears to be due to normal Thysanolaena (Fig. 6) and othergrasses (Miltfluctuationin sampled cell lengthsin maturein- enyi, 1931). Some species have only one interternodes. Mitoticindex decreasesfroman apical node possessingan activeIM at a giventime,almaximumwithan isolatedpeak occurringin mid- thoughin the next older internodecells may still
due to the very be elongatingin the basal region,the formerIM
In6 that is probablyinsignificant
low countit represents.
[e.g., Sobralia (Fig. 8), Flagellaria (Fig. 9), and
Scleria (Fig. 10)].
DIsCUSSION-Differencesbetween intercalary Therefore,we interpret
the IM as a topographand uninterrupted
meristems-The results show ically isolated extensionof the sequence of intertwo contrasting
typesof meristemsin developing nodal meristems.It is part of a developmental
internodes.The IM occurs at the base of the in- continuumstartingat the apex, continuingto
regions, the subapical meristemwhichincludes entireinternode,surroundedby non-meristematic
and cell maturationwithinthe internodeis basip- ternodes,and endingwitha localized basal IM as
confinedto the up- a resultof the elongationand maturationof cells
etal. The UM is progressively
per regionof the internode,continuouswith the in the upper regionsof the internode.There was
subapical meristematicregion, and cell matura- no evidenceof a newlyinitiatedbasal meristemin
tion withinthe internodeis acropetal. Our crite- the older internodessimilar to the "resumptive
meristematic
sitesis thepres- IM" in the gynophoreof Arachis (Jacobs, 1947).
rionfordetermining
ence of dividingcells. Therefore,we feel thatthe
Therewere no IM's in manyspecies. The early
new data presentedin the resultsare particularly stages of internodedevelopmentin these species
activity
of meristematic
significantsince theyshow for the firsttime the have a similardistribution
tissueby direct thatis identicalto specieswhichlaterexhibitIM's.
exact localizationof meristematic
measurementsof cell divisions,as well as histo- The entireinternodeis initiallymeristematicas
logicalchanges(i.e., cell lengthand tissuematura- shownby mitoticindex and cell lengthdata (e.g.,
In12 in Fig. 3, InlO-13 in Fig. 5, and In9-12 in
tion).
For example,in previousinvestigations
of IM's Fig. 13). However,thereis no isolated meriste-
522
AMERICAN JOURNAL OF BOTANY
[Vol. 63
Cyperales
matic area. Meristematicactivitydeclines in the
Cyperaceae* (Buchholz, 1920; Schmalfuss, 1930;
basal region of the internodewith concomitant
Seidel, 1955; Evans, 1965; Fisher, 1970)
acropetalmaturation.The remainingupper meriPoaceae* (Buchholz, 1920; Schmalfuss, 1930;
stematicregionis not an IM because thelowerreMiltenyi, 1931; Sharman, 1942; Ordina, 1952;
gion of thenextyoungerinternodeis stillmeristeKaufman, et al., 1965)
matic,e.g.,In6 and In5 in Fig. 17. In some species
Zingiberales
withnodal vascularplexi,cell divisionmay stopin
Cannaceae (Buchholz, 1920)
the nodal tissuebeforedivisionstops in the upper
Marantaceae*
Liliidae
regionoftheinternodebelow,e.g.,Dioscorea (Fig.
Orchidales
15). However,in such cases thereare neverfully
Orchidaceae (Sobralia) *
maturenodal tissuesbetweenregionsof meristematicinternodaltissues. For convenience,thepatWe muststressthatthe above list is onlyvalid
ternof an initiallyuniformmeristematic
internode
followedby acropetal decline in mitoticactivity for IM's of the shoot internodeand does not inaxis. Of thethree
and acropetalmaturationis referredto as an un- cludethefloweror inflorescence
species of Orchidaceae examined only Sobralia
interrupted
meristem(UM).
In dicotyledonsit would seem that the UM is has an IM. The UM of Vanda and Dendrobium
the common patternof internodedevelopment, may be more typicalfor the family. It appears
based on thefewpublishedstudiesof meristematic thatthereis an IM at thebase of the peduncleor
organizationof internodes. The developingin- inflorescencein many families,e.g., Xyridaceae,
ternodesofSyringaand Helianthus(Wetmoreand Eriocaulaceae, Typhaceae, Amaryllidaceae,and
Garrison,1961; Garrison,1973) have a meriste- related families. However, only developmental
matic regionprogressively
confinedto the upper data on the localization of cell divisioncan unregion. Presumably,the youngerinternodeswere equivocallydemonstratethe presence of an IM.
completelymeristematic.The data showingin- The presence of distinctnodes and sheathing
the
crease in cell numberduringthe gradual acrop- leaves cannot be used alone for determining
meristem
type
(as
seen
in
Table
1).
etal maturationof tissuesin internodesof PhaseoOnly the Commelinidaeand Liliidae of Cronlus and otherspecies (Enrightand Cumbie, 1973;
quist's
(1968) four subclasses of the monocotGrisebach,1843) also indicatethatthese species
withIM's. Although
have UM's. Unfortunately,
many studies on lo- yledonshave representatives
the
Arecidae
the Alismatidae
definitely
lack
IM's,
calizationof internodeextensionby usingsurface
markingsare not usefulin determining
locationof have not been examinedcarefullyenough to be
certain. In generalit is obvious that,otherthan
internodalmeristems.
The data fromsuch studieson internodeexten- the numerousgrassesand sedges,the majorityof
familieswhichhave representasion have shown some variationin growthpat- monocotyledonous
ternsincludingindicationsof intercalarygrowth, tives with elongated internodeslack IM's. The
largertropical groups such as the epiphyticorin species of Apiaceae, Polygonaceae,Caryophylchids, aroids, and palms have UM's, as do most
laceae, and Chenopodiaceae (Grisebach, 1843; othertropicalgroupswe have surveyed.Because
Fahn, 1974). However, there are no published grassesand sedgesare temperateand economically
studies on the distributionof mitoticactivityin important,theyhave been studiedin greaterdethese few examples that would demonstratethe tail than the more numeroustropical monocotpresenceofinternodalIM's.
yledons. This emphasis has lead to erroneous
grass-orientedgeneralizationsabout monocotyleTaxonomicdistribution
of internodalIM-The
donsas a whole.
It maybe tempting
forsome workersto use the
familiesthat have an internodalIM as demonin discusof IM's in monocotyledons
stratedin our survey (shown by asterisks) are distribution
listed below. Citations of previous studies in sions of monocotyledonphylogenysince IM's
which cell length,division, or elongation data seem to occur in the specialized familiesof the
Commelinidae and Liliidae. However, we feel
clearlyshowthepresenceof an IM are also noted.
that such a use of this information
is premature.
The classification
schemeis theLiliatae (= MonoOur surveyonly gives an indicationof the range
cotyledonae) of Cronquist (1968).
and possiblythe distribution
of meristemtypesin
with
internodes.The
species
elongated
vegetative
Commelinidae
occurrenceof boththe IM and UM in one natural
Commelinales
Commelinaceae* (Buchholz, 1920; Scott and family,the Orchidaceae,hintsat the presenceof
Priestley,
1925)
parallel evolutionin the originof elongatedinterRestionales
nodes. The presenceof IM's in the Poaceae and
Flagellariaceae*
some Orchidaceae would also suggestsimilarbut
Restionaceae*
unrelateddevelopmental
phylogenetically
patterns.
Juncales
A detailedsurveyof theinternodalmeristemtypes
Juncaceae (from unreportedobservations)
May-June, 1976]
FISHER
AND FRENCH-MERISTEMS
OF TROPICAL
MONOCOTYLEDONS
523
TABLE 1.
Distribution of families with respect to meristemtypeand morphological characters of the leaf and node
of species examined
Leaf base
Sheathing
Open sheath
Closed sheath
INTERCALARY
MERISTEM
Cyperaceae
Marantaceae
Restionaceae
Commelinaceae
Flagellariaceae
Orchidaceaea
Poaceae
UNINTERRUPTED
MERISTEM
Agavaceae
Araceaed
Pandanaceae
Zingiberaceae
Arecaceae
Costaceae
Orchidaceaee
aSobralia only.
bScleria only.
Cyperus only (Fisher, 1970).
Scindapsus only.
Not sheathing
Nodal vascular plexus
Present
Absent
None
Commelinaceae
Cyperaceaeb
Flagellariaceae
Poaceae
Restionaceae
Cyperaceaec
Orchidaceaea
Marantaceae
Araceae'
Dioscoreaceae
Liliaceae
Philesiaceae
Smilacaceae
Costaceae
Dioscoreaceae
Philesiaceae
Smilacaceaeg
Agavaceae
Araceae
Arecaceae
Liliaceae
Orchidaceae3
Pandanaceae
Zingiberaceae
e Dendrobium and Vanda only.
'Philodendron only, cataphyll sheathing.
gVascular plexus weakly developed.
in the Orchidaceae mightwell clarifythis ques- oftenwith interveningregionsthat are meristetion.
maticallyless active. However,since the mitotic
index does not necessarilyrepresentthe truerate
Significanceof theprimaryelongatingmeristem of cell division(Giffordand Corson, 1971), more
-In his reviewof stemelongationSachs (1965)
reliable methodswill be needed to substantiate
has re-emphasizedthe fundamentalimportanceof this apparentsubapical rise in mitoticactivity.
the subapical meristematic
regionin shoot apices
Duringthe developmentof the IM, theprimary
whichgive rise to most of the cells of the stem. elongatingmeristemin effectis subdividedand
He introducedtheterm"primaryelongatingmeri- extendeddown the axis by its own isolated segstem" to stressthat extensivesubapical meriste- ments,the IM's. Therefore,stemelongationmay
matic regions are responsible for rapid and resultfromtwo different
arrangements
of the priprolongedstem elongationfound in grass inflo- maryelongatingmeristem.It maybe enlargedand
rescences and bolting dicotyledonous species. include many internodes,but it remains a conHowever,he was unable to presentmuch quan- tinuous meristematiczone in which there are
titativeevidencefor such a large subapical meri- UM's. On the otherhand, it may extendfor a
stembecause of the few publishedstudieswhich great distancefromthe apical dome over many
examineddirectlythe regionsof mitoticactivity internodes,mainlybecause of its subdivisioninto
throughout
a shoot. Our studypresentsquantita- IM's.
tive data that fullysupporthis views. All of the
Both the UM and IM are regionsof dividing
species examinedin our studyshow such a pri- cells that are oftenhighlyvacuolated, a characmaryelongatingmeristem,althoughit is present teristicthat is oftenneglectedin generalizations
in varyingdegrees. Climbers such as Gloriosa, about "the meristematic
cell" (Priestley,1929).
Korthalisia,Luzuriaga, and Dioscorea (Fig. 3, 5, The highly vacuolated cells with thin parietal
13, 15) have the largestprimaryelongatingmeri- cytoplasmwhich occur in the IM are similarto
stems in which the meristematicregion extends vacuolated meristematic
cells in active cambium
37.6, 180.6, 18.8, and 45.8 mm, respectively, (Lesham, 1973).
fromtheapical dome.
Morphologicalcorrelationswithmeristemtype
There is a definitesubapicalpeak in mitoticindex greaterthanthatforthe apical dome in many -The distribution
offamilieswithrespectto morspecies (Fig. 3-5, 8-10, 13-20). In otherspecies phologicalfeaturesand meristemtypeis presented
thereis a generaldeclinein mitoticindexfromits in Table 1. Both IM's and UM's occur in species
initialhighin, or adjacentto, the dome (Fig. 23, with sheathingleaf bases that are eitherclosed
24, 25). Thus, if we use mitoticindex as a mea- (formingan unbrokentube), or open (overlap
sure of meristematic
activity,
we findthatin most ping but unfusedmargins). There is no correlaspecies the primaryelongatingmeristemis most tion between type of leaf sheath and meristem
active some distanceaway fromthe apical dome, type. However,the IM is absent in species lack-
524
AMERICAN JOURNAL OF BOTANY
[Vol. 6 3
ing a sheathingleaf base. Althoughthis is not difficulty
in definingdistinctmorphologicalunits
unexpectedsince the basal IM is presumably and the absence of a basal IM. In Alstroemeria
physicallysupportedand protected(as noted by (Alstroemeriaceae),whichpresumablyhas a UM,
Haberlandt, 1914), there may well be other Priestley,Scott, and Gillet (1935) concluded
functionsof the sheathupon theIM, fromtheir analysis of vascular bundle developphysiological
or lightfiltration.There is no cor- mentthatthe shootwas composedof growthunits
e.g.,constraint
relationbetweenpresenceor absence of a nodal extendingthrough16 internodes.Such an intervascularplexus and meristemtype. This is espe- pretationof an internodecomposedof manyovercially evidentin the Cyperaceae in which some lapping units seems highlyartificial,particularly
specieswithan IM have a nodal plexus (Scleria), in light of the continuousprimarilyelongating
and somelack it (Cyperus).
meristemand the UM. In conclusion,the phytoCertainfeaturesof theleaf were also compared mer conceptmay be applicable to certainspecies
withmeristem
type. Presenceor absence of a lig- of grassesand a few othergroups,but it cannot
ule was not correlatedwith meristemtype since
both the ligulate Poaceae and the non-ligulate be applied generallyto monocotyledons.
Cyperaceae and Commelinaceae have IM's. In
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