divide once,tangentially.This produces a row of four cells.The two outermost cellsdifferentiate to become parenchyma cells, while the abaxial inner cell becomes a sieveelementandtheadaxial innercell becomesatrachearyelement.THECULMThe terminal four to seven internodes of the shoot elongate to form the flowering stemorculm,andinternodeelongationiscompletebythetimeofanthesis.Internodesincreaseinfinallengthfromthebaseoftheculmtotheuppermostinternode,whichcarriestheearorthepeduncle (Figure2.1).Thebasal internodes areshorterthanthe enclosingsheath ofthe subtending leaf,whilethe peduncleand the penultimate internode arelongerthanenclosingsheaths,revealingalengthof barestemand carryingtheemerged earclearofthe sheath. Sometimes, in environmentally stressful conditions, internode elongation isrestrictedandtheearremainspartiallyenclosed intheflagleafsheathThe strong, thickened sheaths of the culm leaves are structurally important for stemstrength and stiffness,and theknot or pulvinus is instrumental in carrying theearaloft if theplant is lodged (laid flat usually by wind or rain).AnatomyThe outermost tissue layer,the epidermis,has longitudinal lines of stomata.Itencloses a mechanically strong sclerenchymatous tissue in which, beneath lines ofstomata, are bands of chlorophyll containing parenchyma, similar to the leaf mesophyll.Small vascular bundles also occur in this tissue. The largest bundles are found in theinnermostlayerofparenchymatoustissue(Percival,1921).Thestemissolidatthenodes,butbetweenthenodesthecentral pithbreaksdowntoform an internodal lacuna and the stem is hollow. Vascular bundles are arranged aroundthe internode andrun its full length.Thereare two concentric rings of vascular bundles,those intheouter ringmuch smallerthanthose inthe inner ring.Generally,there are about20bundlesintheinnerringand25intheouterring(Patrick,1972a;Percival,1921)Ateachnode,somebundlesdivergeandentertheattachedleaf,whileotherbundlespass through and enter the next internode. While their route can be traced through thenodal region, bridging strands between the bundles are such that it is thought that therecanbeready interchangeof nutrients at eachnode(Patrick,1972a,1972bHitch andSharman,1971;O'BrienandZee,1971)CulmdevelopmentDuring shoot apex development, all the internodeprimordia (and most of the spikeletprimordia)are initiated before culm elongation commences (usually betweenthe latedouble ridge and terminal spikelet stages). The lowermost internode of what will becometheculmelongatesfirst,followed insuccessionbythenextdistalinternode,thenthenext,andsoon.Elongationispartof coordinated eventsateachphytomerinwhichthelamina,sheathand internodeelongateinawell-ordered succession(Kirbyetal.,1994).14
14 divide once, tangentially. This produces a row of four cells. The two outermost cells differentiate to become parenchyma cells, while the abaxial inner cell becomes a sieve element and the adaxial inner cell becomes a tracheary element. THE CULM The terminal four to seven internodes of the shoot elongate to form the flowering stem or culm, and internode elongation is complete by the time of anthesis. Internodes increase in final length from the base of the culm to the uppermost internode, which carries the ear, or the peduncle (Figure 2.1). The basal internodes are shorter than the enclosing sheath of the subtending leaf, while the peduncle and the penultimate internode are longer than enclosing sheaths, revealing a length of bare stem and carrying the emerged ear clear of the sheath. Sometimes, in environmentally stressful conditions, internode elongation is restricted and the ear remains partially enclosed in the flag leaf sheath. The strong, thickened sheaths of the culm leaves are structurally important for stem strength and stiffness, and the knot or pulvinus is instrumental in carrying the ear aloft if the plant is lodged (laid flat usually by wind or rain). Anatomy The outermost tissue layer, the epidermis, has longitudinal lines of stomata. It encloses a mechanically strong sclerenchymatous tissue in which, beneath lines of stomata, are bands of chlorophyll containing parenchyma, similar to the leaf mesophyll. Small vascular bundles also occur in this tissue. The largest bundles are found in the innermost layer of parenchymatous tissue (Percival, 1921). The stem is solid at the nodes, but between the nodes the central pith breaks down to form an internodal lacuna and the stem is hollow. Vascular bundles are arranged around the internode and run its full length. There are two concentric rings of vascular bundles, those in the outer ring much smaller than those in the inner ring. Generally, there are about 20 bundles in the inner ring and 25 in the outer ring (Patrick, 1972a; Percival, 1921). At each node, some bundles diverge and enter the attached leaf, while other bundles pass through and enter the next internode. While their route can be traced through the nodal region, bridging strands between the bundles are such that it is thought that there can be ready interchange of nutrients at each node (Patrick, 1972a, 1972b; Hitch and Sharman, 1971; O’Brien and Zee, 1971). Culm development During shoot apex development, all the internode primordia (and most of the spikelet primordia) are initiated before culm elongation commences (usually between the late double ridge and terminal spikelet stages). The lowermost internode of what will become the culm elongates first, followed in succession by the next distal internode, then the next, and so on. Elongation is part of coordinated events at each phytomer in which the lamina, sheath and internode elongate in a well-ordered succession (Kirby et al., 1994)
Astheinternodeelongates,theprovascularstrandsare initiated inthecortex andanintercalary meristem develops at the base of each internode. The bundles continuedifferentiation intheupperpart of the internode,whileatthe intercalarymeristem,wherethereisrapidexpansion,protophloemandprotoxylemarefomedanddestroyed.Asmaturity approaches and meristem activity ceases, the bundlescomplete theirdevelopmentandtheinternodal lacunaisformed.TILLERINGThewheatplanthas theabilitytotiller,i.e.toproducelateralbranches.At theendofthe vegetativephase of development, theplantwill consistof,in addition tothemain shoot,anumberoftillers.Exactlyhowmanyarepresentatthisstagevarieswidelydependingonfactors such as plant population, sowing date, mineral nutrition and the application of plantgrowth regulators. Of the tillers present at this time, only a proportion will survive, the restdying without producing an ear, possibly due to competition for resources, such as light ornutrients.NomenclatureIt may be necessary to identify tillers, e.g.for analyses of the effect of tller position ontiller yield. Classification systems generally either number the tillers in a series, starting atthe coleoptile tiller (the first potential tiller) or identify tllers with reference to the leaf inwhoseaxiltheyappear(Petersonetal.,1982:KirbyandAppleyard,1987).Inthelattersystem, which leads to least confusion, the main shoot (MS) bears primary tillers in theaxils of its leaves (Tl in the axil of leaf 1, T2 in the axil of leaf 2, and so on) (Figure2.8). Thetller borne in the axil of the coleoptile is termed TC (TO by some such as Peterson et al.,1982). Each primary tiller has a potential to bear a number of secondary tillers; these aresimilarlylabelledwithreferencetotheprimarytillers,e.g.Ti1isthetillerborneintheaxil ofleaf1oftiller1.Thetillerborneintheaxil oftheprophylliscodedP:thusTCPisthetillerintheaxil oftheprophyll of thecoleoptiletiller.The systemcaneasilybeextendedtohigher-order tillers (e.g.tertiary tillers, T111 or fourth-ordertillers, T1111 and so on)TilleremergenceTillering normally starts when leaf 3 is fully expanded and leaf 4 is emerging on themain shoot with the appearance of the first leaf of T1 above the ligule of leaf 1. Furthertillers are produced in the regular sequence, their appearance coinciding with theemergenceofthethirdleafabovetheleaf subtendingthetiller.Thus,therelationof tillertoleafemergencecanbedescribedintermsofleaforphyllochroninterval,i.e.thenumberofleavesthatemergebetweentheemergenceofaleafandthatof itssubtendingtiller(Friend,1965;Masle-MeynardandSebillotte,1981Klepperetal.,1982).Thephyllochronintervalisgenerallysimilarforalltillerpositions,andtherateofleafemergenceismoreorlessthesame onthemain shootandtillers so thatthepotential increaseinnumbersof tillerperplantcanbe predicted.The behaviour of the coleoptiletiller inthissequenceis often15
15 As the internode elongates, the provascular strands are initiated in the cortex and an intercalary meristem develops at the base of each internode. The bundles continue differentiation in the upper part of the internode, while at the intercalary meristem, where there is rapid expansion, protophloem and protoxylem are formed and destroyed. As maturity approaches and meristem activity ceases, the bundles complete their development and the internodal lacuna is formed. TILLERING The wheat plant has the ability to tiller, i.e. to produce lateral branches. At the end of the vegetative phase of development, the plant will consist of, in addition to the main shoot, a number of tillers. Exactly how many are present at this stage varies widely depending on factors such as plant population, sowing date, mineral nutrition and the application of plant growth regulators. Of the tillers present at this time, only a proportion will survive, the rest dying without producing an ear, possibly due to competition for resources, such as light or nutrients. Nomenclature It may be necessary to identify tillers, e.g. for analyses of the effect of tiller position on tiller yield. Classification systems generally either number the tillers in a series, starting at the coleoptile tiller (the first potential tiller) or identify tillers with reference to the leaf in whose axil they appear (Peterson et al., 1982; Kirby and Appleyard, 1987). In the latter system, which leads to least confusion, the main shoot (MS) bears primary tillers in the axils of its leaves (Tl in the axil of leaf 1, T2 in the axil of leaf 2, and so on) (Figure 2.8). The tiller borne in the axil of the coleoptile is termed TC (TO by some such as Peterson et al., 1982). Each primary tiller has a potential to bear a number of secondary tillers; these are similarly labelled with reference to the primary tillers, e.g. Tl1 is the tiller borne in the axil of leaf 1 of tiller 1. The tiller borne in the axil of the prophyll is coded P: thus TCP is the tiller in the axil of the prophyll of the coleoptile tiller. The system can easily be extended to higher-order tillers (e.g. tertiary tillers, T111 or fourth-order tillers, T1111 and so on). Tiller emergence Tillering normally starts when leaf 3 is fully expanded and leaf 4 is emerging on the main shoot with the appearance of the first leaf of T1 above the ligule of leaf 1. Further tillers are produced in the regular sequence, their appearance coinciding with the emergence of the third leaf above the leaf subtending the tiller. Thus, the relation of tiller to leaf emergence can be described in terms of leaf or phyllochron interval, i.e. the number of leaves that emerge between the emergence of a leaf and that of its subtending tiller (Friend, 1965; Masle-Meynard and Sebillotte, 1981; Klepper et al., 1982). The phyllochron interval is generally similar for all tiller positions, and the rate of leaf emergence is more or less the same on the main shoot and tillers so that the potential increase in numbers of tiller per plant can be predicted. The behaviour of the coleoptile tiller in this sequence is often
anomalous.Undermostconditions,thefrequency of emergence of TC is much lowerthan that of Tl, although it is affected bysowing depth, temperature, nutrient supplyand irradiance.Tiller bud initiation and developmentTiller buds are initiated in the axils of thebasal leaves of the main shoot. The buds inthe axil of the coleoptile and of leaf 1 arepresentintheembryo.Aftergemination,tillerbuds are initiated in the axils of leaves as theyare formed. Buds are usually positionedadjacent totheoverlappingmarginofthesubtended leaf and thus tend to be arrangedhasymmetrically, not on the midline (Williams1975).EachbudbeginsasaridgeoftissueinFIGURE2.8Nomenclatureforleavesandtillersthe axil of the leaf and appears to originatefrom the tissue of the subtended leaf or its disc of insertion.As the tiller bud meristemgrows,theprophyllisinitiatedonitsflanksandenclosestheshootapex.Theprophyllisamodified leaf, which appears to have a similar function to the coleoptile, forming a guide fortheextensionof theyoungleaves enclosedwithin it.Thereisnodevelopmentof thelaminaand it resembles a flattened leaf sheath with two large lateral veins. Subsequentdevelopmentissimilartothatofthemainshoot.Ifthetillerbudcontinuestogrow,thentheprophyllextendstothelengthofthesheathandthefirsttillerleafemerges.Ingeneral,budsarenotformedintheaxilsofleavesthatsubtendanelongatedinternode, except the lowermost node of the elongated stem where a bud is sometimesfound.Where abud ispresent atthis node,the internodes aboveandbeloware short(Williams and Langer, 1975).Tiller bud initiation is related to the development of the subtending leaf. At theemergence of a leaf, the bud that subtends it is about 1 mm long and is visible ondissection(SternandKirby,1979).Iftheenvironmentisunfavourablegrowthquicklyslowsand stops, and the bud does not grow to a length of more than 2 to 3 mm. Underfavourableconditions, leaf and spikelet primordia are initiated at about the same rate as those of themainshoot(SternandKirby.1979)Thereislittlevariationbetweenthemainshootandthedominantprimarytillers(T1,T2andT3)inthenumberofspikeletsinitiatedorinthepatternofprimordiuminitiation.Fewerleaves are formed on T1 thanon the main shoot,and the number of leavesdeclinesprogressively on later formed tillers. Thus the duration of leaf initiation becomesprogressively shorter, and this tends to synchronize the development of ears (Stern andKirby,1979).16
16 anomalous. Under most conditions, the frequency of emergence of TC is much lower than that of Tl, although it is affected by sowing depth, temperature, nutrient supply and irradiance. Tiller bud initiation and development Tiller buds are initiated in the axils of the basal leaves of the main shoot. The buds in the axil of the coleoptile and of leaf 1 are present in the embryo. After germination, tiller buds are initiated in the axils of leaves as they are formed. Buds are usually positioned adjacent to the overlapping margin of the subtended leaf and thus tend to be arranged asymmetrically, not on the midline (Williams, 1975). Each bud begins as a ridge of tissue in the axil of the leaf and appears to originate from the tissue of the subtended leaf or its disc of insertion. As the tiller bud meristem grows, the prophyll is initiated on its flanks and encloses the shoot apex. The prophyll is a modified leaf, which appears to have a similar function to the coleoptile, forming a guide for the extension of the young leaves enclosed within it. There is no development of the lamina and it resembles a flattened leaf sheath with two large lateral veins. Subsequent development is similar to that of the main shoot. If the tiller bud continues to grow, then the prophyll extends to the length of the sheath and the first tiller leaf emerges. In general, buds are not formed in the axils of leaves that subtend an elongated internode, except the lowermost node of the elongated stem where a bud is sometimes found. Where a bud is present at this node, the internodes above and below are short (Williams and Langer, 1975). Tiller bud initiation is related to the development of the subtending leaf. At the emergence of a leaf, the bud that subtends it is about 1 mm long and is visible on dissection (Stern and Kirby, 1979). If the environment is unfavourable, growth quickly slows and stops, and the bud does not grow to a length of more than 2 to 3 mm. Under favourable conditions, leaf and spikelet primordia are initiated at about the same rate as those of the main shoot (Stern and Kirby, 1979). There is little variation between the main shoot and the dominant primary tillers (T1, T2 and T3) in the number of spikelets initiated or in the pattern of primordium initiation. Fewer leaves are formed on T1 than on the main shoot, and the number of leaves declines progressively on later formed tillers. Thus the duration of leaf initiation becomes progressively shorter, and this tends to synchronize the development of ears (Stern and Kirby, 1979). FIGURE 2.8 Nomenclature for leaves and tillers
THEEAREarandearformationAsit approaches anthesis,the earis completelyformedandthe pollengrains andcarpelarefully developed.After anthesis,the florets open,pollen is released and thecarpelsarepollinated.Thestamensand lodicules,theirrolefulfilled,dieand shrivel,andfurther growth and development takes place in the carpels,the developing grains.At thisstage, the ear consists of the main axis or rachis with each internode ovoid in section andcurving around the spikelet. A single spikelet isDead tip of spikeletattachedateachnode,andtherachisterminatesinFloret5a spikelet set at right angles to the lateral spikelets.There is a gradient of size and maturity along theFloret 3ear, with the largest and most advanced spikeletssituatedin themid-part of the ear.UnderPalea J Fioret ILemmiunfavourable growing conditions,the lowermostRachillaspikelet and those at the top of the ear may beowerglumepoorly developed and devoid of fertile florets.Each spikelet comprisesan axis,the rachilla,whichbearstwoglumesandanumberoffloretsRachis(Figure 2.9). Within each spikelet, there are usuallyFIGURE2.9Diagramofaspikeletfromtwotofourpotentiallyfertileflorets.Theflorethas two sheathing structures, the outer lemma andtheinnerpalea;theseenvelopetwolodicules,threestamensandthecarpel(Figure2.10).Eachstamenismadeupofafilamentwhichisveryshortatthisstage,and a yellow anther.Theantherisabout3mmlongandhasfourchambersor loculi containingnumerouspollengrains.The sphericalpollengrainhas a small circular pore and contains a singlenucleus and starch grains (Percival, 1921).The basal part of the carpel, the ovary,isobconical or obovate and white in colour with aFIGURE2.10Transverse section ofa floret,smooth surface except at the tip,which hasshowing the ovary in the centre,surroundedbythree stamens,each antherwith fournumerous unicellularhairs.Theovary containsaloculisingle ovule oriented so that the nucellar apex(micropyle)isslightlybelowthehorizontalmid-planeoftheovule.Theovulehastwointegumentsenclosingthenucellusembeddedinwhichistheembryosac(Percival,1921)The embryo sac contains an egg nucleus with two associated nuclei (the egg apparatus)two polar nuclei and between 20 and 30 antipodal cells, which are highly polyploid (Bennettet al.,1973),The basal florets are generally fertile, but some of the distal florets die sequentiallyduringeardevelopment.17
17 FIGURE 2.9 Diagram of a spikelet FIGURE 2.10 Transverse section of a floret, showing the ovary in the centre, surrounded by three stamens, each anther with four loculi THE EAR Ear and ear formation As it approaches anthesis, the ear is completely formed and the pollen grains and carpel are fully developed. After anthesis, the florets open, pollen is released and the carpels are pollinated. The stamens and lodicules, their role fulfilled, die and shrivel, and further growth and development takes place in the carpels, the developing grains. At this stage, the ear consists of the main axis or rachis with each internode ovoid in section and curving around the spikelet. A single spikelet is attached at each node, and the rachis terminates in a spikelet set at right angles to the lateral spikelets. There is a gradient of size and maturity along the ear, with the largest and most advanced spikelets situated in the mid-part of the ear. Under unfavourable growing conditions, the lowermost spikelet and those at the top of the ear may be poorly developed and devoid of fertile florets. Each spikelet comprises an axis, the rachilla, which bears two glumes and a number of florets (Figure 2.9). Within each spikelet, there are usually from two to four potentially fertile florets. The floret has two sheathing structures, the outer lemma and the inner palea; these envelope two lodicules, three stamens and the carpel (Figure 2.10). Each stamen is made up of a filament, which is very short at this stage, and a yellow anther. The anther is about 3 mm long and has four chambers or loculi containing numerous pollen grains. The spherical pollen grain has a small circular pore and contains a single nucleus and starch grains (Percival, 1921). The basal part of the carpel, the ovary, is obconical or obovate and white in colour with a smooth surface except at the tip, which has numerous unicellular hairs. The ovary contains a single ovule oriented so that the nucellar apex (micropyle) is slightly below the horizontal mid-plane of the ovule. The ovule has two integuments enclosing the nucellus embedded in which is the embryo sac (Percival, 1921). The embryo sac contains an egg nucleus with two associated nuclei (the egg apparatus), two polar nuclei and between 20 and 30 antipodal cells, which are highly polyploid (Bennett et al., 1973). The basal florets are generally fertile, but some of the distal florets die sequentially during ear development
EardevelopmentAfter initiatingleaves,the apex changes in form and initiatesabout 2o spikeletprimordia, terminating in a terminal spikelet (Figure2.5g).Throughout ear development,the most advanced primordia occur in themid-part of the ear.From thedouble ridge stageonwards, the various structures of the spikelet are initiated in a centrifugal succession.Thus, the primordia of the glumes are initiated first, followed in succession by the florets.Abouttenfloretprimordia areeventually initiated,afterwhichthespikeletapex ceasesactivity and eventually degenerates. Thus there is a gradient of development of the floretswithinthespikelet,themostmaturefloretoccurringatthebasewhilethemostdistalfloretsdevelopverylittleandeventuallydie(Plate1)Within the spikelet, initiation also proceeds centrifugally,the lemma and paleaformingfirst and finally the carpel (Barnard, 1955; Williams, 1975). The development of each floretis determinate as the floret apex is transformed into the carpel. As the stamens develop,theybecomedifferentiated intoafilamentand anther,which eventuallyhasfourchambersor loculi containing the pollen grains.As each lobe of the anther develops, a column of archeosporial cells (forerunners ofthe pollen grains)develops by successivemitoses until the pollen mother cells are formedAsthey approachmeiosis,their development is blocked atpre-meiotic interphase andsub-sequent meiosis takes place synchronously (Bennett et al.,1971).Meiosis in the pollenmother cells is concurrent with that of the egg cell in the ovule. Following meiosis, thepollen grains and the embryo sac complete their development (Bennett et al., 1971). Thesynchronyofmeiosisandthetimingofthevarious stageshavebeendescribed indetail(Bennett et al., 1975). Externally, meiosis may be recognized by the presence of greenanthers when the ear is about to emerge from the inflated flag leaf sheath (the boot).Thecarpelisformedbythetransformationofthefloretapex.Afterstameninitiation,aridgeoftissueformsontheflanksoftheapexandacowl-shapedstructuregrowsoverandeventuallyenfoldstheapex,whichthendifferentiatestoformthecarpel.Withintheovule,anarcheosporiumcell differentiatesand eventuallybecomesthemegasporemothercell(Barnard, 1955). As the carpel continues to develop, the tip grows out to fom a two-lobedstigma, each one profusely branched.AnthesisAnthesisoccursaboutthreetotendays,dependingontheenvironment,aftertheearemergesfromtheflagleaf sheath,whenanumberof closelycorrelated eventsoccurinavery shorttime.Thelodiculesof eachfloret swell up,forcingapartthelemmaandpaleaThefilamentsof thestamens elongateandmayeventuallyattaina lengthof about10mmAs the filament grows, the anther dehisces,each chamber developing a longitudinal split,startingatthetipoftheanther,throughwhichpollenisreleased.Thestigmalobes,whicharepressedtogetherbeforeanthesis,moveapart,andthereceptivebranchesarespreadwidely giving a large area for pollen interception. The whole process is complete withinabout five minutes (Percival, 1921).Cultivars differ in the degree to which the lemma and palea are separated, and insome closed-flowering types, the lemma and palea do not diverge,the anthers and stigma18
18 Ear development After initiating leaves, the apex changes in form and initiates about 20 spikelet primordia, terminating in a terminal spikelet (Figure 2.5g). Throughout ear development, the most advanced primordia occur in the mid-part of the ear. From the double ridge stage onwards, the various structures of the spikelet are initiated in a centrifugal succession. Thus, the primordia of the glumes are initiated first, followed in succession by the florets. About ten floret primordia are eventually initiated, after which the spikelet apex ceases activity and eventually degenerates. Thus there is a gradient of development of the florets within the spikelet, the most mature floret occurring at the base while the most distal florets develop very little and eventually die (Plate 1). Within the spikelet, initiation also proceeds centrifugally, the lemma and palea forming first and finally the carpel (Barnard, 1955; Williams, 1975). The development of each floret is determinate as the floret apex is transformed into the carpel. As the stamens develop, they become differentiated into a filament and anther, which eventually has four chambers or loculi containing the pollen grains. As each lobe of the anther develops, a column of archeosporial cells (forerunners of the pollen grains) develops by successive mitoses until the pollen mother cells are formed. As they approach meiosis, their development is blocked at pre-meiotic interphase and sub-sequent meiosis takes place synchronously (Bennett et al., 1971). Meiosis in the pollen mother cells is concurrent with that of the egg cell in the ovule. Following meiosis, the pollen grains and the embryo sac complete their development (Bennett et al., 1971). The synchrony of meiosis and the timing of the various stages have been described in detail (Bennett et al., 1975). Externally, meiosis may be recognized by the presence of green anthers when the ear is about to emerge from the inflated flag leaf sheath (the boot). The carpel is formed by the transformation of the floret apex. After stamen initiation, a ridge of tissue forms on the flanks of the apex and a cowl-shaped structure grows over and eventually enfolds the apex, which then differentiates to form the carpel. Within the ovule, an archeosporium cell differentiates and eventually becomes the megaspore mother cell (Barnard, 1955). As the carpel continues to develop, the tip grows out to form a two-lobed stigma, each one profusely branched. Anthesis Anthesis occurs about three to ten days, depending on the environment, after the ear emerges from the flag leaf sheath, when a number of closely correlated events occur in a very short time. The lodicules of each floret swell up, forcing apart the lemma and palea. The filaments of the stamens elongate and may eventually attain a length of about 10 mm. As the filament grows, the anther dehisces, each chamber developing a longitudinal split, starting at the tip of the anther, through which pollen is released. The stigma lobes, which are pressed together before anthesis, move apart, and the receptive branches are spread widely giving a large area for pollen interception. The whole process is complete within about five minutes (Percival, 1921). Cultivars differ in the degree to which the lemma and palea are separated, and in some closed-flowering types, the lemma and palea do not diverge, the anthers and stigma