The consequence is that there are a considerable number of species in which the grain has been described by some as adherent and by others as free, and which have consequently been transferred from one genus to another. Yet, if not taken too absolutely, the character is sometimes a useful one, assisting, for instance, in the arrangement of the genera of some of the subtribes of the difficult tribe Festuceæ.

Considerable importance was attached by the earlier agrostologists to the presence or absence of the awn on the back or apex of the flowering glume; but this has subsequently been found to be subject to great variations. The spiral twist, however, in the lower part of the awn in some genera is more constant, and in the 'Flora Australiensis' I had taken it as an essential character of some tribes or subtribes; but there are more exceptions than I was then aware of. The awn, when present, is generally twisted in Andropogoneæ, Tristegineæ, Agrostideæ, and Avenaceæ, and not in Paniceæ, Chlorideæ, Festuceæ, or Hordeæ; but it is sometimes very slightly so in a few species of the latter group, and in the former tribes, where the awn is much reduced, if there be any twist it is scarcely perceptible. In all the tribes, also, the awn is occasionally, and in the straightawned ones frequently, altogether deficient ; and in some genera, as in Stipa for instance, where it is usually twisted, there are exceptional species in which it is straight or curved only. The character must therefore generally be used with more or less of reservation.

The partial or absolute separation of the sexes or the increase in the number of stamens observed in a few genera have been occasionally introduced amongst tribual characters; but further observation has shown that they occur amongst Gramines of very different affinities, and have thus proved to be often of no more than generic value, although in one tribe, the Maydeæ, the absolute unisexuality of the spikelets may be constant.

Differences in the size of the embryo, in the form of the socalled scutellum on the caryopsis (indicative, apparently, of the hilum of the seed), or in the longitudinal groove or cavity frequently observable on the caryopsis, have been sometimes brought forward as absolute generic, if not tribual, characters, and they may often be really important; but we know, as yet, too litɩle about them to test their value fairly. Herbarium specimens rarely supply ripe fruits, and they have been carefully observed

and accurately described in comparatively few species. The characters thus ascertained in a single one have been supposed to belong necessarily to the whole genus; and when differences have afterwards been found in some other species, it has at once been generically separated, without ascertaining whether these differences might not be reconciled or connected through other species. Before, therefore, we can ascertain the real generic value of characters which cannot be tested in herbarium specimens, it is necessary that we should have them well and authentically described in a much greater number of species from actual observation. I have on several occasions had reason to believe that, in long-detailed descriptions drawn up by accurate botanists from dried specimens, the seminal characters have been rather guessed at on theoretical grounds, than actually verified on really ripe seeds.

Following out the views of General Munro as to the general arrangement of the Order in as far as I have been able to ascertain them, we have divided it into tribes and subtribes, of which the following are the most prominent characters, omitting for the present exceptional forms, which occur in almost all of them :

A. PANICACEE. Spiculæ cum pedicello infra glumas articulatæ, flore fertili unico terminali, addito interdum inferiore masculo v. sterili.

Tribus i. Paniceæ. Spiculæ hermaphroditæ, rarius abortu unisexuales, spicatæ v. paniculata, rhachi inflorescentiæ inarticulata. Gluma florens exaristata, fructifera indurata v. saltem exterioribus rigidior. Tribus ii. Maydeæ. Spiculæ unisexuales, masculæ terminales spicatæ v. paniculatæ v. (in Pariana) fœmineam circumdantes, fœmineæ inferiores spicatæ, cum rhacheos internodio (excepta Zea) articulatim secedentes.

Tribus iii. Oryzeæ. Spiculæ hermaphroditæ v. rarius unisexuales, paniculatæ v. spicatæ, rhachi inflorescentiæ inarticulata. Gluma sub flore summa (palea?) uninervis v. carinata.

Tribus iv. Tristegineæ. Spiculæ hermaphroditæ, secus paniculæ ramulos inarticulatos solitariæ v. rarius geminæ v. fasciculatæ, cum pedicello articulatæ. Gluma vacuæ aristata v. muticæ, florens hyalina v. tenuiter membranacea, arista geniculata terminata v. mutica. Tribus v. Zoysieæ. Spiculæ hermaphroditæ v. nonnullæ imperfectæ, cum rhachi inarticulata spicæ simplicis sigillatim v. fasciculatim articulatæ. Gluma florens membranacea, sæpius vacuis minor hyali

naque.

LINN. JOURN.-BOTANY, VOL. XIX.

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Subtribus 1. Anthephoreæ. Spicule in pedicello 3-∞, in fasciculum deciduum confertæ. Gluma florens nunc vacuis sublongior, nunc brevior hyalina.

Subtribus 2. Euzoysieæ. Spiculain pedicello solitaria, rarius gemina. Gluma florens vacuis brevior, hyalina.

Tribus vi. Andropogoneæ. Spicula secus spicæ rhachin v. paniculæ ramulos, sæpissime geminæ v. terminales ternæ, in quoque pari homogamæ v. heterogamæ. Gluma florens vacuis minor, hyalina, sæpe aristata.

B. POACEE. Pedicellus infra glumas continuus. Rhachilla supra glumas inferiores persistentes sæpe articulata, ultra flores fertiles producta, stipitiformis v. glumas vacuas v. flores imperfectos ferens, v. interdum flos fertilis more Panicacearum unicus terminalis, sed cum gluma sua a vacuis persistentibus articulatim secedens.

Tribus vii. Phalarideæ. Flos hermaphroditus unicus, terminalis. Glume 6 (v. 5 et palea) uninerves v. carinatæ.

Tribus viii. Agrosteæ. Spiculæ l-floræ, rhachilla ultra florem nuda v. in setam v. stipitem producta.

Subtribus 1. Stipex. Panicula laxa v. irregulariter spiciformis. Gluma florens arista sæpius terminata, fructifera caryopsin arcte involvens. Rhachilla ultra florem non producta.

Subtribus 2. Phleoideæ. Panicula spiciformis densa, cylindracea v. subglobosa. Gluma florens mutica v. aristis 1–3 terminata fructifera caryopsin laxe includens. Rhachilla interdum producta.

Subtribus 3. Sporoboleæ. Panicula laxa v. ad racemum reducta, rarissime spiciformis. Gluma florens mutica. Caryopsis demum sæpius glumis apertis subdenudata. Rhachilla non producta. Subtribus 4. Euagrosteæ. Panicula varia, sæpius laxa. sæpius arista dorsali instructa, rarissime mutica. laxe inclusa. Rhachilla sæpe producta.

Gluma florens Caryopsis gluma

Tribus ix. Isachneæ. Spiculæ æqualiter biflora. Glumæ sæpius muticæ. Rhachilla ultra flores non producta.

Tribus x. Aveneæ. Spiculæ bi- v. plurifloræ, sæpius paniculatæ. Glumæ florentes arista dorsali v. interdum terminali sæpissime instructa. Rhachilla ultra flores sæpius producta.

Tribus xi. Chlorideæ. Spiculæ uni- v.

plurifloræ, secus rhachin spica

rum unilateralium biseriatim sessiles, secundæ.

Tribus xii. Festuceæ. Spiculæ bi- v. plurifloræ, varie paniculatæ v. rarius racemosæ. Glumæ florentes muticæ v. aristis terminatæ. Subtribus 1. Pappophoreæ. Gluma florentes plurinerves tri- pluriaristatæ, v. absque aristis quadriloba.

Subtribus 2. Triodieæ. Gluma florentes uni- v. trinerves, tridentatæ, trifida v. triaristatæ.

Subtribus 3. Arundineæ. Rhachilla sub glumis florentibus longe pilosa. Subtribus 4. Seslerieæ. Inflorescentia spiciformis v. capituliformis, basi glumis vacuis v. spicis sterilibus sæpius stipata. Stylus v. rami sæpius longi tenues.

Subtribus 5. Eragrosteæ. Gluma florentes trinerves. Cætera normalia. Subtribus 6. Melicex. Gluma florentes tri- v. plurinerves, superiores duæ v. plures vacuæ, semet involventes.

Subtribus 7. Centotheceæ. Folia plana, lanceolata v. ovata, inter venas transverse venulosa. Gluma florentes quinque- v. plurinerves.

Subtribus 8. Eufestuceæ. Gluma florentes quinque- v. plurinerves. Cætera normalia.

Tribus xiii. Hordeeæ. Spiculæ uni- v. plurifloræ, ad dentes seu excavationes rhacheos spicæ simplicis sessiles.

Subtribus 1. Triticeæ. Spicula ad nodos solitariæ, tri- v. pluriflora, rarius biflora.

Subtribus 2. Leptureæ. Spiculæ ad nodos solitariæ, uni- v. biflora. Spica tenuis.

Subtribus 3. Elymeæ. Spiculæ ad nodos geminæ v. plures collaterales. Tribus xiv. Bambuse Gramina elata, sæpius basi saltem lignosa. Folia plana, sæpissime cum vagina articulata. Spiculæ uni- v. plurifloræ. Lodiculæ sæpius 3. Stamina 3, 4, v. plura.

Subtribus 1. Arundinarieæ. Stamina 3. Palea bicarinata. Pericarpium tenue, semini adnatum.

Subtribus 2. Eubambuseæ. Stamina 6. Palea bicarinata. Pericarpium tenue, semini adnatum.

Subtribus 3. Dendrocalameæ. Stamina 6. Palea bicarinata. Pericarpium crustaceum v. carnosum, a semine liberum.

Subtribus 4. Melocanneæ. Stamina 6 v. plura. Palea 0 nisi glumis simillima. Pericarpium crustaceum v. carnosum, a semine liberum.

I now proceed to a more detailed revision of the several tribes, subtribes, and genera, in the order in which I have worked them up for the forthcoming part of our Genera Plantarum,' to which I must refer for the technical characters and references, as well as for the synoptical clavis of the genera.

Series A. PANICACEE.

This first main division of Gramineæ is very fairly defined by the combination of two characters-the articulation of the pedicel below the spikelet or cluster of spikelets, and the single fertile flower apparently terminal, with or without a single male or sterile one below it. Where either of these two characters fails, the plant should be referred to Poaceæ.

The articulation of the pedicel is usually immediately below

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the lowest glume, leaving, as the spikelet falls away, a slight dilatation or callosity at the apex of the persistent portion. Sometimes it is not easily observed at the time of flowering, but becomes more marked as the fruit ripens. A similar marked articulation has not hitherto been observed in Poaceæ, except in Fingerhuthia. There are also a very few cases where the lowest glumes are reduced to slight callosities, or are so rudimentary as to render it difficult to say whether the articulation is in the pedicel or in the rhachilla. In the Cenchrus group of the tribe Paniceæ, in the subtribe Anthephores of Zoysieæ, and in some Andropogoneæ, the articulation is not under each spikelet, but under a little cluster of two or more spikelets; and in Maydeæ it is the rhachis of the spike which disarticulates under each female spikelet. In Gramineæ generally, however, the articulation, whether of the rhachis, of the pedicel, or of the rhachilla, is usually under the fertile spikelets or flowers only; under the males it is apt to be very obscure or quite obsolete.

The fertile flower is above spoken of as only apparently terminal, because the presence of the palea and a slight obliquity tend to show that the floral axis is not really the continuation of the rhachilla, but, as in Poaceæ, a secondary or axillary branch. Doell says, indeed, that a continuation of the rhachilla behind the palea has been observed in a species of Panicum; but I have never succeeded in meeting with it in any Panicaceæ. In the tribe Oryzeæ, where there is no two-nerved palea, it may still remain a matter of doubt whether the floral axis is or is not distinct from the rhachilla-whether the uppermost scale is a glume on the rhachilla or a palea at the base of the floral axis. The presence or absence of a central nerve is not an absolute test; for it is occasionally, though very rarely, absent in the lower glumes.

Panicaceæ have never more than four glumes, the uppermost one usually enclosing or subtending the fertile flower, though in some Andropogoneæ it is excessively reduced or even quite obsolete or rudimentary. The next under it may be empty like the lower ones, or may enclose a palea, a rudimentary flower, or a perfect male flower, and in Beckmannia, and a very few species. or individuals of Setaria and Panicum, this lower flower may be hermaphrodite, but usually, if not always, sterile. The two lower glumes when present are always empty. Where the spikelets are unisexual, the females have only the single terminal flower, the males most frequently two flowers, both with perfect

stamens.