108 Botanisches Centralblatt. — Beiheft 2. 



not only of the same deep bluish-green, but also differentiated 

 into very distiuct grains, somewhat larger tlian those contained 

 in the palisades. When treated with iodine the cell-content of 

 both sheaths beeomes almost black like that of the palisades, the 

 reaction thus being identically the same. In other species we 

 observed the color of the cell-content in the sheaths to be much 

 less marked when compared with that of the palisades, for instance 

 in A. piirpurascens, where the sheaths and palisades possessed 

 Chlorophyll of exactly the same shade, and a similar uniformity 

 in color was also observed in some other species: A. desmantha^ 

 A. Reverchonü etc. We have noticed this difference in color and 

 consistency of the cell-content of the sheaths so often, that we 

 are almost inclined to think that the Variation may possibly 

 depend upon the age of the leaf, rather than characteristic of 

 certain species. It must also be remembered that the material, 

 which we have studied was in many cases not fresh, but had 

 been dried or preserved in alcohol for several years. 



In A. dichotoma Mich-K., the only representative of Beau vais' 

 y^Curtopogoii"', the structure agrees in all respects with that of the 

 species of the section Chaetaria, described above. The bulliform 

 cells are large, and the mestome-bundles are constantly small and 

 orbicular in outline ; the inner sheath is a little thick-walled in 

 contrast to the outer one, and the color of the Chlorophyll was 

 observed to be deep bluish-green in both. A similar structure 

 occurs in the two species of „Streptachne"" : A. divergens Vas. and 

 A. Sckiedeana Trin., which are, thus, inseparable from Chaetaria 

 anatomically ; but while, the cell-walls of both sheaths are very 

 thin in the latter species, those of the inner one are quite thick 

 in A. divergens^ and the cells of this contain no Chlorophyll, 



Aristida californica Thurb., A. desmantha Trin. and A. tubev 

 culosa Nutt., all indigenous to North America, belong to the group 

 forming ßeauvais' genus ^Arthratherum"" , since they possess an 

 articulated aAvn, which, however, is glabrous in contrast to that 

 of the other species of bis genus, in which the awns are plumose. 

 Their leaf structure, however, is identical with that of the other 

 sections or subgenera, as described above, and the double paren- 

 chyma-sheath is very distinct in all three species. But the leaves 

 of the other species of Arthratherum with plumose awns (by 

 Bentham and Hook er and Hacke 1 refered to Nees' 

 ^Stipagrostis^) show a very different structure, which in all respects 

 agrees with the descriptions and illustrations of some of these 

 species in the works of Duval-Jouve and Volke ns (1. c). 



In these the mesophyll is arranged as in the preceding 

 species, but borders here on a large-celled parenchyma-sheath 

 with Chlorophyll, inside of which is no secondary green sheath, 

 but only a layer of thick-walled mestome-parenchyma. There 

 is the appearance of a mestome- sheath in the largest of the nerves, 

 where this thick-walled parenchyma Covers both the leptome and 

 hridrome as an almost continuous sheath. But since this sheath 

 is not preseut in the smaller bundles, and since it does not resist 



