116 Botanisches Centralblatt. — Beiheft 2. 



ridges developed into long, pointed hairs, which cover the furrows, 

 where small bulliform cells are observable ; the stomata are sunk 

 below the surface of epidermis and are located in the farrows. — 

 Minor groups uf stereome occur also on the upper face of the 

 blade, above the mestome-bundles, connecting these with epidermis. 

 The mesophyll represents a homogeneous tissue of roundish cells 

 with no palisades around the mestome-bundles. These, the mestome- 

 bundles, are surrounded by a thin-walled, colorless parenchyma- 

 sheath and a mestome-sheath, continuous in all the bundles, with 

 heavily thickened inner cell-walls: all the mestome-bundles are 

 located in the projecting ribs, while the compact mesophyll 

 occupies the furrows. 



Fijotochaetium Presl. 



P. bicolor Desf. (Grassy fields, Montevideo, Uruguay). 



F. lasianihum Griseb. (Stony ground , Montevideo, 

 Uruguay). 



P. stipoides Hack. (Grassy fields, Montevideo, Uruguay). 



P. tuherculatum Desv. (Grassy fields, Montevideo, Uru- 

 guay). 

 The leaves of this genus differ from those of Nassella especially 

 by the epidermis, which consists, here, of relatively large cells on 

 the dorsal face of the blade, between the groups of stereome^ 

 which does not form a continuous cover as we have described 

 above as characteristic of Nassella. Furthermore the ventral 

 epidermis is in Piptochaetium plainly diiferentiated into relatively 

 broad bands of bulliform cells, located in the deep furrows between 

 the prominent ribs. The lower face is sraooth and glabrous in 

 contrast to the upper, where short, prickle-like projections from 

 the epidermis abound above the midrib and along the margins. 

 The stomata occupy the same position as in Nassella. 



The stereome is, then, much less developed in this genus 

 than we observed in Nassella, and, moreover, it is often separated 

 from the mestome-bundles by layers of mesophyll, especially in 

 the lateral portions of the leaf-blade. While the mesophyll in 

 Nassella was composed of a homogeneous tissue of roundish cells, 

 we find in Piptochaetium, distinct palisades radiating towards the 

 Center of the mestoi je-bundles. 



The parenchyma-sheath is destitute of Chlorophyll and the 

 cells are relatively narrow and thin-walled ; it is continuous in all 

 the bundles and borders directly on a similarly closed mestome- 

 sheath with moderatel}^ thickened cell-walls ; thick-walled mestome- 

 parenchyma was observed as a single layer between the leptome 

 and hadrome. 



Piptochaetium bicolor possesses the broadest leaf of these four 

 species and the number of mestome-bundles averages about five 

 on each side of the midrib, while in the other species, of which 

 the leaves are very narrow, almost capillary, the number of nerves 

 is only three in all, one on each side of the midrib; they, the 

 mestome-bundles, are orbicular in all the species, when considered 

 in transverse section. 



