Silica grains in woody plants of the neotropics, especially Surinam

36 Pages·2012·3.46 MB·English

Silica grains in woody plants of the neotropics,
especially Surinam
B.J.H. ter Welle
InstituteofSystematic Botany,
University ofUtrecht, The Netherlands
Summary. Distributionpatterns, frequency,size, shape, andsurface textureofsilica grainsinthesecondary
xylem of neotropical taxa, especially from Surinam werestudied extensively. Over 2000 sampleswere
examined. Silica grains occurin about 300 species (32 families and about90genera).Thegrainsproved
tobepresentin many taxa sofarconsidered asnon-siliceous. Theyaremost frequentlyfoundintheparen-
chymatous tissues (in 80% ofsiliceous material studied, grains were presentin the ray cells). Theirdis-
tribution isvery constant,especially whentheyarerestrictedtoonetypeoftissue,althoughsomeexceptions
exist. The diagnosticvalue ofthe silica grains, oftenneglected,appearstobe very high.The shapeofthe
grains is usuallyvariable though,in a few cases it is very characteristic. Various types ofsurface struc-
tures are recognized. Size ofthe grains is reported.The great variation in grain size greatly reduces its
importanceasadiagnostictool.
INTRODUCTION
In 1857Criiger forthefirst timedescribedthe occurrence ofsilicagrains inthesecon-
dary xylem of some species in what is nowrecognized as the family oftheChryso-
balanaceae. The presence ofsilica has since been thesubject of manyinvestigations
(Klister, 1897; Petrucci, 1903; Gonggrijp, 1923, 1932; Prison, 1942; Besson, 1946;
Amos, 1951, 1952; Bamber & Lanyon, 1960; Burgess, 1965; Balan Menon, 1965;
Murthy, 1965;Sharma&Rao, 1970; Hirataetal., 1972; Scurfield etal„ 1974a, 1974b).
Some investigators have attempted to evaluate the taxonomical significance of the
presence ofsilica, whereas others primarily dealtwith sometechnicalaspects such as
a possible correlationbetweentheoccurrence ofsilicagrains andtheresistance ofthe
timbertomarineborersorbetweenthepresenceofsilicaanddifficultiesencounteredin
sawing timbers.
By using saws made from special steel and sawing underwet conditions, using logs
completely soaked with water, mostproblems caused bysilicainclusions were solved.
Theeffect ofthesilicagrains on the resistanceto marine borers is onlysmall, as canbe
judged by theresults of investigations carriedoutby Southwell& Bultman(1971) who
examined over ahundredspecies.
The diagnostic importance of silica grains, consideredby Amos (1952) as a very
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B. J. H. TER WELLE
promising subject, is still ofinterest although mostwood anatomiststake thevalueof
this character as aboutequal to thatofacomparable featurelike thepresence ofcrys-
tals. Most articles on this subject are restricted to geographical regions inAfrica and
Asia. Only Gonggrijp (1923) andAmos(1951) reported theoccurrence ofsilicagrains
in a few neotropical species. In hisworldwidesurvey Amos (1952) included only 44
species with silica inclusions from theneotropics, 20species belonging to theChryso-
balanaceae.Thepresentinvestigation thereforeis focussedontheneotropics; especially
Surinamwoods werestudiedbecauseofagoodrepresentation intheUtrechtcollection.
MATERIALS AND METHODS
All woody species fromSurinamrepresented inthewood collectionofthe Instituteof
Systematic Botany of the University of Utrecht were investigated. Besides, a great
numberofspecies fromGuyana andFrenchGuianawere includedinthepresentstudy.
Whensilicagrains were foundin aSurinamrepresentative ofa family, theotherneo-
tropical generaofthatfamily were studiedas well. Mostofthefamiliesnotfoundinthe
Guianas, but represented in our wood collection were also examined. About 2000
samples (c. 75 families, c. 440 generaandc. 1300species) were investigated. Allwood
samples are backed by herbariummaterial,which is deposited, for thegreaterpart, in
the Institute ofSystematic Botany oftheUniversity ofUtrecht. Inaccordancewith an
earlier study(terWelle, 1976) samples forsectioning were takenfrom awoodblockof
theheartwood.
To study thesilica distribution, radial sections of 15to 25/umthick were prepared.
The sectioning was donewithoutany pre-treatment, only cold waterwas used.After
sectioning the sections were bleached with adomestic bleaching agentfor oneortwo
minutes, thenrinsedinwaterandheatedincarbolicacid, andfinallymountedincloveoil.
In addition scanning electron microscopy (SEM) was used to obtainbetter infor-
mationabout thesurfaceofthe grains.
Although various types of siliceous inclusions occur in the secondary xylem this
investigation is restricted totheoccurrence and distributionofsilicagrainsonly.
RESULTS
No silica grains were observed in the familiesand generalistedinTable2.Species in
which silica grains occur are described as follows: the dataon the distributionofthe
grains, the locality and the source ofthe specimens are given inTable 1; size, shape,
frequency, and additional data of a given species or genus are reported below. The
families are treatedin alphabetical order. Pertaining data from the literatureare in-
cluded.Non-siliceous generaofthefamiliesare listedattheendofeachfamily descrip-
tion. The numberofspecies investigated is given betweenbrackets.
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SILICA GRAINS
ANACARDIACEAE
Silica grains arepresentinallspecies ofAnacardium.Grains globular with asmoothor
a granular surface, maximumsize 10 to onegrainpercell,buttherearealso cells
withoutagrain.DePaula& deHamburgoAlves(1973) didnotreportanythingaboutthe
presenceofsilicainA.spruceanum.Inthematerial ofLoxopterygium sagotii somewood
specimens containsilica grains, others do not.Grainswereabsent in eight offourteen
samples investigated (BBS12- v. Hall57-LBB10734;Lindeman5841,6057,6080,6194,
6856; BAFOG198M). They werepresent inthesamples listedinTable1.Grains nearly
always globular withasmoothsurface, size5 to lOftm.Nosilica grains wereobserved
in Schinus(1), Spondias (1), Tapirira (2),and Thyrsodium (2).
BOMBACACEAE
ThegenusBombax s.l. comprises both species with and species withoutsilica grains.
Grains globular with a granular surface, size normally upto 15 butsometimesas
large as 23pm, one grain percell, but notin every cell. Species withoutsilicagrains;
B.flaviflorum, B. globosum, and B.surinamense.AccordingtoAmos(1952),whostudied
5 species, Bombax is non-siliceous. If the classification of Robyns (1963), whosplit
Bombax into several genera, is followed all genera comprise siliceous and non-
siliceous species. All species ofQuararibea containsilicagrains, in theray cellsaswell
as intheaxialparenchyma. Grainsglobular withamoreorlesssmoothsurface, sizeup
to 15fim.Thegrains occurmorefrequentlyintheaxialparenchyma thanintheray cells.
Nosilicagrains wereobserved in Catostemma(2),Ceiba(1),Matisia(1), andScleronema
(1).
BONNETIACEAE
The family concept followed hereis that of Maguire (1972). Silica grains occur inall
samples of two genera, viz. Archytea and Haploclathra. In Archytea the grains are
globular and sometimesthey assume other shapes, the surface is smooth, size ofthe
globular grains 3to 15 theoval/oblongonesupto 30 X Normallythey occur
intheprocumbent ray cells, butsporadically also inthe upright ray cells. Thegrainsin
Haploclathra are mostly globular andtheirsurfaceislesssmooththaninArchytea.They
measure 3 to 13 De Paula(1974) noticedsilica inHaploclathra but consideredits
occurrence in this genusof no taxonomicvalue. Threespecimens ofKielmeyera were
studied. Silica grains are present in only one specimen. Two types of grains were
found: (1) globular, with asmooth surface andacompactstructure(size upto8/im);
(2) irregular, the grains look like a cluster of small silica particles glued together.
Baretta-Kuipers(1976) whostudiedthesamewoodsamplesreports differencesinother
anatomicalcharacters between thesample with andthe samples withoutsilica.
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B. J. H. TER WELLE
No silica grains were observed in Bonnetia(3), Caraipa (3), Mahurea(2), Marila(2),
andNeblinaria(1).
BURSERACEAE
In this family silica grains occur in the ray cells, axial parenchyma cells, fibres
and/or tyloses of the vessels. Their distribution pattern is very variable.Grains in
Dacryodes are globular, oval or oblong with a granular surface; the globular grains
measure upto m,theoblongonesupto25 X 12ftm.InParaprotium thegrainsoccur
inalltissues except thevessels. Grainsofvariousshapes, theglobularonesupto 17ftm.
Protium is a genus in whichbothspecies withand species withoutsilicagrains arere-
presented. The non-siliceous species are; P. alstonii, P. aracouchini, P. crassifolium, P.
glabrescens, P. hostmannii, and P. pullei. The grains, when present, are sometimes
restricted torays or parenchyma only; sometimesthey are foundinall tissues. Grains
usually moreor less globular, withagranular surface, size upto 18ftm,butsometimes,
as inP. insigne, they donotexceed5 ftm. Insomecases they looklikeaclusterofsmall
silica particles glued together. Thefourthgenus containing silicais Trattinickia. Here,
too, the distributionpattern is very variable, butin allspecies grains occur intheray
cells, although oftenrestrictedto themarginalray cells(Plate 1/4).Grainsmoreorless
globular with agranular surface, size 11 to22ftm. Webber(1941) didnot recordsilica
grains in herwood anatomicalstudy oftheBurseraceae.Nosilicagrainswereobserved
in Canarium(1), Hemicrepidospermum (1), and Tetragastris (4).
CARYOCARACEAE
Silica grains are present in all species investigated of Anthodiscus. Grains nearly
globular, size up to 13 pm. The grains in the axialparenchyma resemble thoseinthe
rays. No silica grainswere observed in Caryocar (6).
CHRYSOBALANACEAE
Theoccurrence ofsilicagrains in the secondary xylem was reported for thefirst time
by Criiger(1857) insomespecies ofthisfamily. A worldwidesurveyonthedistribution
pattern of silica grains in this family was madeby terWelle(1976). All species inves-
tigated contain silica (Plate 1/1-2). The following generawere included in the in-
vestigation: Acioa, Chrysobalanus Couepia, Exellodendron Hirtella, Licania and
, , ,
Parinari.
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SILICA GRAINS
CONNARACEAE
Silicagrains occur inPseudoconnarusandRourea. Grains globular, with agranular sur-
face, size up to23pm.Theoccurrence ofsilica grains in thisfamily is not reported by
Metcalfe& Chalk(1950), Amos(1952) nor by Dickison(1972). AccordingtoMennega
& Veenendaal(unpublished results) all samples ofAgelaea from Cameroonshow the
same silica distributionpattern as Pseudoconnarusand Rourea. An africanspecies of
Connarus, C. griffonianus, unlike the neotropical species ofthis genus, contains silica
in theray cells. No silica grains were observed in Cnestidium(1) and Connarus(6).
ERYTHROXYLACEAE
Outof ninespecies ofErythroxylon investigated, E.squamatumis theonly oneinwhich
no silicagrains wereobserved.The grainsare globular, ovaloroblong. Allshapes may
occur inthe same sample. Their size and shape are often determinedby the sizeand
shape oftheray cellsandthey may filluptheentirecell.Thesurfaceisgranular,except
in E. citrifolium;; in this species grains witha granular and grains with amoreor less
smoothsurfacemay occur sideby side.Consequently thesizeishighlyvariable,butthe
grains are always large(up to 50 x 20/um), except inE.citrifoliumwherethemaximum
size is 15 Each oftheprocumbent ray cells contains oneor two grains; intheup-
right marginal ray cells, grains maybepresentor absent, but thereis nevermorethan
one grain per cell. In theliteraturethe occurrence ofsilicagrains inthis family is not
reported(Record & Hess, 1943;Metcalfe& Chalk, 1950;Normand, 1950;Amos, 1952;
Brazier& Franklin, 1961).The presenceofsilica grainsisperhaps restrictedtotheneo-
tropical species as asample from NewGuinea(E. ecarinatum) studied by me, isalso
devoidofsilica.
EUPHORBIACEAE
In three genera, Actinostemon, Maprounea, and Senefeldera the occurrence ofsilica
is aconstant feature. Actinostemonand Senefeldera are two alliedgenerawhichshare
the same characteristic silica distribution pattern. The silica grains, whichoftenfill
the entireray celllumen, havea granular surface andthey measure upto60 x 25
The oblong grains are more frequent than theglobular grains.
In Maprounea they aresmall(about 3/rm)andofvariousshapes. Sometimesthey suggest
a clusterofsmallsilica particles glued together. Species with andspecies withoutsilica
grains occurjnMicrandra. Grainsglobular, withagranular surface,ovaloroblong, size
oftheglobular grainsup to23/am, size oftheoblongones upto 30 x 13pm.InM.elata
from Surinamthe grains are very small(3 Intwo species, M. glabra andM. spru-
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B. J. H. TER WELLE
ceana no silica is present. These two species, formerly included inthegenus Cunuria,
were transferredto Micrandra by Schultes (1952). Webster (1975) reinstatedCunuria.
The silica distributionseems a featurein favourforkeeping the two generaapart.
No silica grains were observed in Acalypha (1), Alchornea (1), Alchorneopsis (1),
Amanoa(1),.Aparisthmium'(I).Chaetocarpus (\),Conceveibai(2).Croton(12),Drypetes(2),
Fluggea (1), Glycydendron(1), Hevea(3),Hura(1), Hyeronima(1),Jatropha(1),Mabea(3),
Manihot(1), Margaritaria (1), Micrandropsis {1),Omphalea (1), Pausandra(1), Pera(2),
Phyllanthus (4), Piranhea (1), Plukenetia-(1), Sagotia (1), and Sapium (2).
FLACOURTIACEAE
The wood anatomy of the Flacourtiaceae was extensively studied by Miller(1975),
whoreported silica grains in the ray cells ofMayna amazonica (size 10 to 16pm)and
Lindackeria laurina. All othergenerafromthe neotropics lack silicagrains. Thisobser-
vation is in agreementwith my own investigation of species from the Guianas.
GUTTIFERAE
Only one species of Clusia, C. palmicida containssilicagrains. Grains globular,small,
2to 10,um, mostly 2to 5pm; surfacemostly smooth. Sometimesthe grains looklike
a cluster ofsmallsilicaparticles gluedtogether. Grainswere not reported by dePaula
(1974). In the sample ofOedematopus quadratus investigated smallsilicagrainswitha
granularsurface(size 3pirn)arepresent. Anunidentifiedsample ofthesamegenusdid
not containsilica.
In fourteen species of Tovomita investigated silica grains occur, whereassix other
species lack silica (T. choisyana, T. obovata, T. pittieri, T.plumeri, T. rileyi, and T.
rubella). Grains normally globular withagranular surface, size 3to 15pm,sometimes
up to 25pm,never morethanoneperray cell. Probably thegrains donot occur inthe
uniseriate rays. According to de Paula (1974) the occurrence of silica grains is a
constant featureofallspeciesofTovomita.Theherbariumvouchersofthenon-siliceous
species were checkedby Mrs. A. R. A. Gdrts-van Rijn. Thereis no doubtthat they
belong to this genus.
No silica grains were observed in Calophyllum (1), Havetia (1), Moronobea(1),Plat-
onia (1), Rheedia(3), Symphonia (1), and Thysanostemon (1).
HIPPOCRATEACEAE
The wood anatomy of this family was described by Mennega (1972). Ofthetwelve
generainvestigated the monotypic genusPrionostemmawastheonly oneinwhichsilica
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SILICA GRAINS
grains were found.They are restricted to theray cellsandmostlyshowaglobularshape
but other shapes are present as well. Their surface is granular and they measure up
to23 pm.This is one ofthe fewlianas knownsofar to possess silica grains.
No silica grains were observed in Anthodon (1), Cheiloclinium (4), Cuervea (1),
Elachyptera (1), Hemiangium (1), Hippocratea (2), Hylenea (1), Peritassa (3), Pristi-
mera (3), Salacia (9), and Tontelea(2).
HUMIRIACEAE
Only one species ofSacoglottis, S. guianensis, contains silicagrains in both ray cells
and axial parenchyma cells. No differenceinsilica grain distributionwas notedinthe
formasandvarietiesofthisspecies describedbyCuatrecasas( 1961).Grainswithagranu-
lar surface, mostly globular, sometimes(BBS 117 andKrukoff6653) ofothershapes;
sizeoftheglobular grains3to 13 sometimesupto 18 ovalonesupto20x 15,um;
thereis never morethanonegrainpercell, intheaxialparenchyma therearealso cells
without a grain. In two species (S. amazonicaandS. cydonioides) nosilicagrainswere
observed.Theoccurrence ofsilica grainsinthisfamilywasnotreportedbefore(Metcalfe
& Chalk, 1950; Amos, 1952).
Nosilica grains were observed in: Humiria(1), Humiriastrum(1), Schistostemon(1),
and Vantanea(2).
LAURACEAE
Silica grains occur in four neotropical genera. In Cryptocarya they looklikeacluster
of smallsilica particles glued together. The grains are small(ca. 5 Inthegenus
Licaria three species studied havesilica grains; twelve species were foundtobewith-
out silicagrains (L. amara,L. aritu,L. armeniacum,L. aurea,L. canella, L. cayennense,
L. debilis. L. guianensis, L. martiana, L. multiflorum, L.polyphylla, andL. vernicosa).
Grains globular to oblong, witha granular surface, globular ones2 to25pm,oblong
ones upto 45 X 25 InMezilaurusitaubatheyareglobular(3to withagranu-
larsurfaceandtheyoccuronly inpartoftheray cells.Thereisnevermorethanonegrain
per cell. Insome samples the grains are grouped together in subdividedprocumbent
ray cells(Plate 1/5). In these cell familiestheirsize is about thesamealthough with-
in one sample it varies much. This distribution pattern, according to Amos (1952)
uniqueto Mezilaurus, was not noticedinM. synandra. Herethegrainsareglobular with
a more or less smooth surface and measure 3 to 13 ,um. Two species of Ocotea, O.
glaucinia and O. splendens, containsilica grains inthe fibres.Thefibresare septateand
normally each compartment contains one grain. The grains measure 5 to 15 fim. In
contrast, afurther twenty-six species of Ocotea, are without silica.
No silica grains were observed in Aniba (10), Beilschmiedia (1), Endlicheria (3),
Nectandra(4), andSystemonodaphne (1).
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B. J. H. TER WELLE
LEGUMINOSAE
Silicagrains occur in theray cellsand/oraxial parenchyma cells inthreegeneraofthis
family. InDialiumguianense they arerestrictedtotheaxialparenchyma. Grainsglobular
with a granular surface, size upto 15 sometimesup to 20,um; allparenchyma cells
containone grain each. The distributionpattern ofthegrains inDicorynia is quite dif-
ferent fromthat inDialium. Here the grains occur bothin ray cells andparenchyma
cells. Grains globular withagranular surface,sizeupto28/x mintheraysaswellasinthe
axial parenchyma. In the rays the grains occur only in the marginal cells. Normally
there is one, but sometimes there are two or three grains per cell. Four species of
Sclerolobium were investigated. Two ofthem, S. albiflorum and S. guianense, contain
silica grains in the ray cells and sometimes in the axial parenchyma. Grains globular
witha granularsurface, size upto 15pminS.albiflorum andupto22juminS. guianense.
The two other species, without silica grains, are S. melinonii and S. micropetalum.
According to Koeppen (1967) a few other generafrom the neotropics containsilica,
e.g. Apuleia and Tachigalia.
Nosilica grains wereobserved inAlexa(2), Aldina(1),Anadenanthera(1),Andira(6),
Bowdichia(1), Caesalpinia (1),Calliandra (1), Campsiandra (1),Cassia(2),Cedrelinga (1),
Clathropis (1), Copaifera (1), Crudia (2), Cynometra (2), Dahlstedtia(1), Dalbergia (5),
Derris(4), Dimorphandra (2), Diplotropis (2), Dipteryx (4), Elizabetha(2), Enterolobium
(2),Eperua (3), Erythrina (1), Etaballia(1), Gliricidia (1), Heterostemon(1), Hymenaea
(1), Hymenolobium (2),Lecointea(1),Lonchocarpus (9),Machaerium(3),Macrolobium(4),
Marmaroxylon (1), Martiodendron(1), Mora (2), Ormosia (5), Palovea (1), Parkia (2),
Peltogyne (2),Piptadenia (2),Piscidia(2),Pithecellobium(9),Platymiscium(1),Poecilanthe
(1), Pterocarpus (4), Samanea (1), Sesbania (1), Stryphnodendron (3), Swartzia (5),
Tephrosia (1), Vatairea(1), Vataireopsis (1), Vouacapoua (1), and Zygia (2).
LECYTHIDACEAE
The silica grains in the Lecythidaceae show a great variation in shape, size, and
frequency. They mostly occur in therays and sporadically intheaxialparenchyma and
inthe tyloses ofthe vessels. The grainsare globular, oval, or oblong. Sometimesonly
oneshape occurs inasample, in aspecies or inawholegenus,butoftensamples appear
to containall shapes. Thecells normally containone grain, butsometimes, although
sporadically, cellswith twograins areseen;inadditionacertainnumberofcellswithout
grainsare always found.Thegrains inAllantomaare globular and measureupto m.
All species investigated of Carinianacontainsilica grains in the rays and sometimes
in the parenchyma. Grains mostly globular, sometimes oval or oblong, size of the
globular grains upto20/um, sizeoftheoblong ones upto35X 20pm;insamples which
contain globular grains only, the grain size is 3 to 13pm\ small grains often showa
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SILICA GRAINS
smoothsurface unlike thebigger onesthesurfaceofwhichisgranular. Thegrainsinthe
axial parenchyma ofC. pyriformis are smallerthan those in the ray cells ofthesame
sample. In Corythophora thegrains are globular with granular surface, andare upto
13 pm in size. The silica grains in Couratari are restricted to the ray cells. Their
frequency is variable, sometimes they areabundantand sometimesthey are sporadic.
Grains mostly globular, sometimes oval or oblong, always large, size of theglobular
ones up to 20,«m(partly upto 30 theoblong ones measure upto 30 x 15/um or
even upto40X 20fim,andinC.stellata{Krukoff8893 )upto80 x m. Generallythe
grains inCouratariare larger, moregranular, moreoblong andlessfrequentthanthose
in Cariniana.
Thirty species ofEschweilera were analysed. Infourspecies; E. chartacea, E. conges-
tiflora, E. poiteaui, and E. roroda silica grains were never found. In one species, E.
simiorum, foursamples were analysed, two ofwhichappeared tocontainsporadic silica
grains in therays, whereastheothertwo lacked silica grains. Allotherspecies investi-
gated of Eschweilera, however, show a large amount of grains in the rays. Grains
globular, oval or oblong, size oftheglobular ones 4to20pm,sometimes25 to30pm,
oblong grains mostly 25 x 10/imto 30 x 20pm, sporadically upto40 x 15/xmoreven
up to60 X 15,umin two samples ofE. obversa.
In Holopyxidium jaranum globular grains (up to 18 and oblong grains (up to
50 X 20 /tm) were observed, but H. latifolium {IANw 3879) on the contrary lacks
silica.
Six species ofLecythis were investigated. Grainsofsporadic occurrence (Plate 1/3)
mostly oval, square or oblong and sporadically globular, always large, size ofthe
globular ones upto 18to25 oblong onesfrom45 X 20,umto70 x 20/um. Thegrains
are usually restricted to the ray cells, butthere aretwo exceptions: Lecythis peruviana
contains silica grains in the ray cells and also in theparenchyma cells. Besides, these
grains are muchsmallerthanthoseintheotherspecies ofLecythis andtheiroccurrence
is abundant, contrary tothe few grains present intheotherspecies. InL. gigantea (two
samples) nosilica grainswereobserved.Dr. G.T.Prance(NewYorkBotanicalGarden)
studied the herbariumvouchers ofthese twospecies. In his opinion the samples are
probably referabletoEschweilera.
No silica grains were observed in Asteranthos (1), Bertholletia(1), Couroupita (8),
Grias(I), and Gustavia(4).
MELIACEAE
Silica grains occur in two generaof this family. BothGuarea and Trichilia comprise
species withand species withoutsilica. Atotalof fifteen species ofGuarea was investi-
gated, six of these contained silica grains in the ray cells. Grains mostly globularbut
other shapes are present too, size oftheglobular grains upto 18pm andthe sizeofthe
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B. J. H, TER WELLE
oblong ones upto 35 x 15/im;theglobulargrains arecompactwhilethosewithvarious
shapes are moreor lessloosely built.According toAmos(1952) small silicainclusions
occur in the ray elementsofGuarea fromNigeria, Ivory Coast, and BritishHonduras.
The grains in the samples investigated by me are large. In an African species like G.
laurentiiagain large grains are found(up to 15 ,um). Species ofGuarea withoutsilica
grains are G. alborosea, G. borisii, G. costata, G. davisii, G. duckei, G. kunthiana, G.
pohlii, G. pubiflora, and G.rhabdotocarpa. OnlythreeoutofnineteenspeciesofTrichilia
investigated are without silica grains, T. casarettii, T. grandifolia, and T. elegans. The
grains are for the greaterpart globular and upto 12 except in T. trinitensis(upto
20jum).As in Guarea, both compactandlooselybuiltgrainsnormally occurinthesame
sample, but, in Trichilia,these loosely built grains are more frequent than in Guarea.
Thereis never morethan onegrain per cell,and grains do not occur in each cell.
The origin ofthe specimens of Trichilia investigated by Amos(1952) is not known.
Two species were studiedand were reported as non-siliceous. An African species,
T. lancei, examinedduring thepresentinvestigation containssilicagrainsintheraycells.
Apparently thedistributionofsilicagrains is not restrictedtotheneotropical species
of Trichilia. According to Amos (1952) and Pennington & Styles (1975) afew other
generacontain silicagrains. Nothing is said by these authors abouttheir taxonomic
importance.
Nosilica grainswere observedinCabralea(2), Carapa (2), Cedrela(2), andSwietenia
(3).
MENISPERMACEAE
The wood anatomy ofthis family was studiedby Mennega(1977). Silicaproved tobe
present only intwospecies ofAnomospermum: A. bolivianumandA. solimoesanum. On
the contrary three other species of this genus lack silica. Grains globular with a
granular surface, size up to 13,um. They occur in both rays andaxial parenchyma.
Silicagrains were not observedinthirteenother generainvestigated by Mennega.
OLACACEAE
The occurrence ofsilica grains in this family isrestrictedto the ray cellsofonegenus,
Liriosma. Grains globular and sometimesoval or oblong with a granular surface, size
10to28nm.Someray cells lack silicabutcontainacrystalinstead.According toAmos
(1952) this family is largely non-siliceous, although somespecies may contain small
quantities ofsilica.
No silica grains were observed in Chaunochiton (2), Heisteria (2), Minquartia (1),
and Ptychopetalum (1).
116