214 Botanisches Centralblatt. — Beiheft 2. 



•ecting ribs, and are constantly arranged in one plane, alternately 

 arge and small. They are mostly oval in transverse section. 



A green parenchyma-sheath surrounds each bnndle. It is 

 ■closed in all the nerves and thin-walled excepting in the larger 

 mestome-bundles, wliere sometimes two or three cells on the 

 leptome - and the hadrome - side may exhibit a thickening of 

 the cell-walls, but only where the stereome borders directly on 

 this sheath. Inside the parenchyma-sheath is a typieal closed 

 mestome-sheath ofwhich the inner cell-walls are distinctly thickened 

 in the larger mestome-bundles of all these species This structure 

 of the parenchyraa - and the mestome-sheath was observed in 

 •our specimens of the genus, and not only in the species with 

 naked awns, but also in those, where this organ is plumose. In 

 a, Word, the double parenchyma-sheath is wanting in 8tipa\ at 

 least in the species, enumerated above. And neither Duval- 

 J o u V e , G ü n t z , S c h w e n d e n e r or V o 1 k e n s (1. c), who 

 have also studied some species of the genus, raake any mention 

 of the presence ot a double parenchyma-sheath. Only the mestome- 

 sheath has been recorded by Prof. Schwenden er as occurring 

 in Stipa pennata and tortüis, to which may be added those, we 

 liave enumerated above. 



Oryzop SIS Michx. : 



0. asperifolia Michx. (Rieh woods, New-York). 

 0. canadensis Torr. (Plains, Minnesota). 

 0. melanocarpa Muhlbg. (Rocky woods, Minnesota). 

 0. micrantha Thurb. (Plains, Denver, Colorado). 



The leaves are quite broad andflat in the two species from wood- 

 lands : asperifolia and melanocarpa, but narrow in the two 

 others. The general structure of the leaf is very uniform in these 

 species and is suggestive of that, which we have described above 

 as characteristic of Stipa. We observe also in the leaves of 

 Oryzopsis a smooth, more or less scabrous lower face in contrast 

 to the Upper, which is furrowed and usually provided with long, 

 scattered hairs. The furrows are deepest and narrowest in the 

 tw^o species from the plains. In 0. melanocarpa a midrib is plainly 

 visible by its larger support of stereome and by containing more 

 mesophyll than the others, but no bulliform cells or colorless 

 parenchyma is developed above the midrib as is otherwise fre- 

 quently observed in Gramineae with broad, flat leaves. The bulli- 

 form cells constitute very small groups, viewed in transverse 

 section, in the bottom of the furrows of the narrow-leaved species, 

 while in those with broader leaves these cells are not only larger, 

 but they also form groups of much greater width than in the 

 others. 



The stomata are mostly to be found on the sides of the 

 furrows and are level with the epidermis in 0. asperifolia and 

 melanocarpa , but sunk (below epidermis) in the two others. 

 Stereome is especially well developed in 0. micrnntJia, where it 

 ^ccompanies the mestome-bundles, and is observable on either face 



