Mr. Woods on the Genera of European Grasses. 17 



Grasses, but we do not notice it unless it occur in a remarkable degree, as in 

 the glumes of P/mlaris and Rechniannia. This may be accompanied with a 

 keel, as in the first instance, or be without one, as in the second, and conse- 

 quently a form may be both navicular and keeled {glumce navlculares carinatœ), 

 but not intermediate between them. 



The distinctions which appear to me to be useful are: 



Involute. The margins turned in, as in the palese of Stipa, and perhaps of 

 most of those Grasses where the outer palea hardens on the seed. 



Concave. Rounded at the back, as in the paleœ of the Panicecc. This 

 occurs sometimes where the organ is nerved or ribbed, as in Glyceria uqua- 

 tica, but rarely where there is a keel or midrib decidedly stronger than the 

 other ribs. 



Compressed. The two sides meeting in an angle at the back ; this generally, 

 but not necessarily includes a midrib. The outer paleœ of Pua and Dacti/Us 

 may furnish examples. 



The first of these may exist in union with either of the others, and to any 

 of them a keel may be added: two or three terms may therefore be used in 

 the same description, but they should not be compounded. 



In some Grasses we find the glumes or palese of even texture throughout; 

 in others we find nerves, as in the palese of the Paniceœ, where they are quite 

 unaccompanied by any elevation of the surface. I cannot call these strise, 

 because there is in some cases a closely and uniformly striated surface ; yet 

 they show themselves only in colour. In others we find, as in Gh/ceria, 

 Eragrostis, and some species of Poa, sharply prominent nerves, and in others, 

 as Scleroclihu, a thick rounded nerve, or almost indeterminate thickening of 

 the substance with intermediate hollows, which do not seem always deep 

 enough to be called furrows. The first of these I call nerves, the latter, ribs. 

 In all these cases the outer palea, to which these particularities of description 

 chiefly apply, has a central nerve or prominence, to which I do not give the 

 name of midrib, uidess it be stronger or more prominent than the others. 



The inner palea has usually two ribs, at which the membrane is foldeil in 

 upon the parts of fructification. While in flower it almost uniformly follows 

 the curve of the outer palea, at least in Grasses where the spicula has more 

 than one flower, till the swelling of the seed forces it into a line concave 



VOL. XVIII. D 



