The tribes composing the series of Panicaceæ run much into each other, and have been very variously extended or reduced. We have adopted the following six, as having appeared to us to be rather better defined than the smaller or larger ones that have been proposed.

Tribe I. PANICEÆ.

The principal character of the Paniceæ, considered as a tribe of Panicaceæ, consists in the hardening of the fruiting glume. In several of the smaller genera, however, and even in some species of Panicum itself, it is membranous, but usually larger than the outer ones, and forming the chief covering of the fruit, never hyaline or much reduced as in Andropogoneæ. Oryzopsis, Milium, and their allies, which were formerly included in Paniceæ, have been transferred to Agrostides on account of the persistent lower glumes below the articulation. Among the other general characters of the tribe, the inarticulate rhachis of inflorescence is constant except in Stenotaphrum, where, however, the articulation is very tardy and not constant, so that it has often been denied. The flowering glume never bears the twisted awn, so general in Andropogoneæ and Tristegineæ, although in Eriochloa and a very few species of Panicum its obtuse apex has a short, erect, almost dorsal point; the awns of Oplismenus, Chataria, the section Echinochloa of Panicum, &c. are straight and terminate one or more of the empty glumes only. The fertile flower terminating the spikelet is, in the normal genera, either perfectly hermaphrodite, or, at any rate, as far as I have observed, has staminodia round the pistil. It is only in a few of the abnormal genera added to the tribe that there are strictly female spikelets.

The normal genera of the tribe may be distributed in four rather distinct groups, though scarcely marked enough to be raised to the rank of subtribes; and to these we would add a few more or less abnormal genera, but little connected with each other, but all apparently more nearly allied to Panicea than to any other tribe.

In the first group, or Paniceæ proper, we have distinguished eleven genera-a number somewhat arbitrary; for much might be said in favour either of uniting the whole into one vast genus Panicum, or of dividing them still further, as some have proposed, into about twice as many as those here adopted, the distinctive characters being often either very uncertain, or such as are not universally recognized as generic in the Order.

1. REIMARIA, Flügge.-This old-established and universally acknowledged genus has generally been limited to two tropical and subtropical American species, with a peculiar slender habit and inflorescence, and characterized by having only one empty glume below the flowering one, and by the constant reduction of the number of stamens to two. It has since, however, been ascertained that several species which cannot well be separated from Paspalum have only a single lower empty glume; and Doell has distinguished Reimaria chiefly by the reduction of the stamens, together with the form of the spikelets more acuminate and more closely appressed to the rhachis than in any Paspalum. He has added, under the name of R. aberrans, a third species, which, with a more vigorous habit, rather invalidates the natural distinction from Paspalum, but has all the characters of Reimaria; and Munro recognizes a fourth species, allied to R. aberrans, but with only two, or at most three, spikes to the panicle and a much thicker rhachis, in the Florida plant distributed by Curtis with the number 3566 as Paspalum vaginatum, but probably not the one entered under that name in Chapman's 'Flora of the Southern United States.' It occurs also in Wright's Cuban collection under n. 3854, and may be characterized as R. oligostachya, Munro, spicis in pedunculo 2 rarius 3 (nec 6-15), rhachi dilatata spiculis sublatiore. The true Paspalum vaginatum, Sw., is a synonym of P. distichum, Linn.

2. PASPALUM, Linn., ranks among the large genera of tropical Gramineæ, and in respect of the greater number of species is a natural one, readily distinguished from Panicum by the inflorescence and by the technical character of the deficiency of the small lowest glume. It is now, however, ascertained that neither character is quite constant. A few Panica of the section Brachiaria have the inflorescence of Paspalum ; and the lowest glume is frequently reduced to a small callus, or is entirely deficient in the section Digitaria; and the consequence has been, that several species have been referred by some botanists to the one genus and by others to the other. These ambiguous species appear, however, to be best placed in Panicum ; and all true Paspala bave the spikelets sessile or nearly so, in two or four rows along the lower or outer side of the rhachis of the spikes or simple branches of the panicle, and they show no trace of the small lowest glume of Panicum. Thus defined, the number of species may be estimated at about 160, by far the greater proportion of them tro

pical American, a few of which are also generally spread over the warmer regions of the Old World, especially P. distichum, Linn. (P. vaginatum, Sw.), which reaches southern Europe as an introduced weed. Scarcely five species can be regarded as belonging exclusively to the Old World. The above estimate of the total number is founded chiefly on the investigations of Munro, who had nearly completed the working-up of the genus, and has left full descriptions with diagnoses and synonymy of 138 species, besides a few that he had left for further inquiry. Steudel enumerates 262 species, but nearly half of them have proved to be mere synonyms or very slight varieties. Doell describes in detail 105 Brazilian species; but some of them are what I cannot consider as really distinct; and his own views of them were any thing but stable, as there are several which he at one time referred to one species and later transferred to another, forgetting to eliminate them from their former place, thus :

Gardner, n. 2354, is repeated under P. malacophyllum and P. subsesquiglume.

Hostmann, n. 658, under P. densiflorum and P. cæspitosum. P. distachyum, Salzmann, n. 667, under P. pumilum and P. divergens.

Gardner, n. 3496 and 3497, under P. maculosum and P. notatum. Gardner, n. 2975, under P. vaginatum, P. tropicum, and P. filifolium.

P. cespitosum, Hochst., n. 1543,
P. amazonicum, Trin., and
P. humile, Steud.,

Digitaria uniflora, Salzm., n. 659,
and Spruce, n. 679,

P. surinamense, Hochst., n. 1283, scoparium.

under P. plicatulum and P.

dissectum.

under P. platycaulon and

P. furcatum. under P. furcatum and P.

Spruce, n. 30, under P. chrysodactylon and P. chrysoblephare.

Fournier enumerates 40 Mexican species, of which thirteen are described as new; but he is, in Gramineæ, generally disposed to admit as distinct species forms which I perfectly agree with Munro in regarding as slight varieties, corresponding to what so many local European botanists describe as critical species.

With regard to the subdivision of the genus, Trinius, in his several revisions, distributed the species chiefly according to the size of the spikelets, which, however much it may affect the general aspect of the species, is in many cases far too uncertain a character to be practically useful. Nees, in his 'Agrostologia Brasiliensis,' proposed six sections, which Doell reduced to four,

Munro, though he had so nearly completed his descriptions of species, and often indicated the sections to which he referred them, had not yet definitively grouped them, leaving his manuscripts, for convenience of reference, in alphabetical order.

have adopted three sections, founded on Nees's, which appear to us well defined by positive characters-Eupaspalum, Cabrera, and Anastrophus, subdividing the first, and largest, into four groups or subsections, Anachyris, Opisthion, Pseudoceresia, and Ceresia, much less marked in their outlines, but generally speaking fairly natural.

Eupaspalum comprises the great majority of the species, and is distinguished by the spikelets strictly secund along the rhachis of the spikes, with the back of the flowering glume and of the lower empty one (when present) turned outwards-that is, away from the rhachis or from its midrib; whilst in Anastrophus, which includes the remainder of the genus except the monotypic Cabrera, the spikelets are almost distichous, and the back of the flowering glume and of the lower empty one turned towards the midrib of the rhachis. This distinction was specially relied upon by Nees under the terms spiculæ adverse and spiculæ inverse, and followed up by Doell. It is not alluded to by Fournier with regard to the Mexican Paspala; but, if I understand correctly his words (Gram. Mex. p. vii), it nearly corresponds to the character he proposes for the primary division of Gramines.

Anachyris, the first subsection of Eupaspalum, is a purely artificial one, characterized solely by the having only a single empty glume below the flowering one. It was first proposed as a genus by Nees for the Paspalum malacophyllum, Trin., which has all the habit and floral and other characters of Paspalum except this single one; and Fournier, apparently on this account, transfers it to the tribe Oryzea. Doell, however, reduces it to a section of Paspalum under the name of Eremachyrion, associating with it a few other species, some of them evidently more nearly allied to corresponding species of the section Opisthion than to each other. And even the technical character is not always constant; for in P. (Eremachyrion) sesquiglume, Doell, a species closely allied to P. (Opisthion) maritimum, Trin., I frequently find a minute outer glume; and, again, P. pallidum and P. candidum, H. B. K., both of which Doell places in Eremachyrion, are scarcely to be distinguished from each other except by the lowest empty glume absent in the one, present in the other, as originally pointed out by

Kunth. Nees describes the palea (upper palea) of the typical Anachyris paspalodes or Paspalum malacophyllum as 3-nerved; Fournier says it is 1-nerved. The species is very variable as to the size of the spikelets, the hairs or setæ on the rhachis of the spike, &c.; but in all the specimens I have examined I have uniformly found the palea normally 2-nerved.

Opisthion, proposed by Doell as a section of Paspalum, is our second subsection of Eupaspalum. It includes all the typical Paspala with two lower empty glumes, and the rhachis of the spikes not dilated. The species are numerous and varied, but scarcely reducible to distinct groups.

Pseudoceresia is a subsectional name I should propose for the genus Ceresia as understood by Elliott and other North-American botanists. In it the rhachis of the spikes is more or less dilated and concave, but green and herbaceous throughout, and the spikelets are small and glabrous or nearly so. The species are few, including P. stoloniferum, Bosc, P. repens, Berg., and their allies. Ceresia is the name we would reserve for our fourth subsection, being the genus Ceresia as originally established by Persoon, in which the dilated rhachis of the spikes is bordered by a coloured or smooth membranous margin, and the half-enclosed spikelets are larger than in Pseudoceresia and densely ciliate. Besides several Brazilian and other tropical species, it includes the Mexican P. cymbiforme, Fourn.

Cabrera, our second section of Paspalum, is limited to the single P. aureum, H. B. K. (not of Trinius), forming Lagasca's genus Cabrera, in which the direction of the spikelets is nearly that of Anastrophus; but instead of being marginal on each side of the rhachis, they are deeply embedded in alternate cavities on each side of the midrib, on the outer or lower side of that rhachis. This remarkable arrangement is very well described by Lagasca, who was a most accurate botanist. His 'Nova Genera et Species Plantarum,' forming part of the 'Elenchus Horti Matritensis,' is a model for the clearness and conciseness of the characters given, which are most thoroughly to be depended upon. The work is quoted by Nees and by Doell, but evidently at second hand; had they really read it, and had they studied Kunth's good figure and description, they could never have given to the P. aureum the new name of P. immersum, or have transferred the synonym of Cabrera chrysoblepharis, Lag., to the P. exasperatum, Nees, or to the supposed distinct P. chrysoblepharis, Doell, both of them at