THE BLUEGRASSES. 17 



most species are thin and translucent, or hyaline. The extent of the 

 hj^aline portion of the apex has much to do with the form of the latter 

 and is variable in the different species. 



The palea is commonly more delicate in texture than the glume, 

 being- partially hyaline. It usually is shorter than the glume, but in 

 some species equals or exceeds it in length. The difference in length 

 usually is most evident in the lower florets of the spikelet. Two veins 

 traverse the palea lengthwise and nearly meet at its apex. The -mar- 

 gins of the palea are more or less acutely infolded along these veins, 

 which are called the keels of the palea. The keels are mostly covered 

 by the glume in some species, while in others they are almost wholly 

 exposed. There is some variation in this respect, however, among 

 seeds of the same species. The apex of the palea is often notched. 



The rachilla segment is nearly cylindrical and usually somewhat 

 curved. It is slightly expanded at the apex, which is obliquely trun- 

 cate, its terminal surface constituting the scar of at- 

 tachment to the succeeding floret. Diflerent florets in 

 the same spikelet in certain species exhibit a marked 

 variation in the length of the rachilla segment, which 

 is shortest in the lower florets and conspicuously 

 longer in the terminal one, where it usuallv bears an 

 aborted floret as a small, pointed appendage. 



The surface of the florets of dift^'erent species of Poa 

 is subject to considerable variation. Some florets are 

 smooth, or glabrous; others bear numerous minute, 

 stiffish hairs, rendering the surface rough, or scabrous; "^KentuTk? bre*^ 

 and some have a tine, appressed pubescence covering grass seed {Poa 

 a part of the surface. Most of the species have a f «'™^'')^ «■ ^^^b; 



^ _ i &, pubescence of 



more or less silky pubescence on the keel and mar- marginal vein; c, 

 ginal veins below the middle or somewhat higher on pu^t>escenee of 

 the keel. The intermediate veins are more rarely 

 pubescent. The keels of the palea are usually fringed with minute 

 hairs, or are hispid-ciliate, but in some species they are silky pubes- 

 cent. The basal web is wholly wanting in some species and in others 

 varies from a few fibers to a copious tuft. It readily separates from 

 the floret in most species. The rachilhx segment is usually smooth, 

 but in some species it is appressed pubescent. The presence of the 

 hairs on the marginal veins often necessitates that care be used in 

 examining the rachilla segment Avith respect to pubescence. (Fig. 2.) 

 The color of mature seeds varies from verv light brown to dark 

 brown. Sterile seeds are usually lighter or straw colored. Immature 

 seeds are more or less tinged with green; some are purplish. Jn cer- 

 tain species the glume is tinged with golden yellow near the apex. 

 The al)orted terminal floret and all the hairs are white. The rachilla 

 segment is lighter colored than the glume or palea. 

 5813— No. 84—05 3 



