104 Botanisches Centralblatt. — Beiheft 2. 



fasciculata lack a mestome-sheath, there exist in the larger of 

 these some thick-walled cells on the leptome-side in the shape of 

 an arch, besides a single layer between the leptome and hadrome, 

 but these cells proved to be thick walled mestome-parenchyma. 



In comparing this leaf-structure with that of other genera of 

 Gramineae we have failed to find a corresponding case where two 

 parenchymatic and chlorophyll-bearing sheaths occur inside radially 

 arranged palisades. The outer of these sheaths represents, no 

 doubt, the ordinary parenchyma-sheath, which surrounds all the 

 mestome-bundles in the Gramineae, and which lies close up to 

 the adjoining palisades, whether a mestome-sheath is present or 

 not ; but in regard to the inner sheath of larger cells we can not 

 at present designate this by any other name than „an inner 

 parenchyma-sheath", though we prefer to speak of them both 

 unitedly as „a double sheath". 



It was, at first, our thought that the innermost of these sheaths 

 might be morphologically analogous to the very similar one, 

 which has been described by Haberlandt, Rikli and the 

 writer as characteristic of no small number of Cyperaceae, but 

 for reasons to be mentioned later, we have relinquished, this idea. 



Leaf-structure oi Aristida in general. 



Continuing our study of A. fasciculata we might mention 

 the other tissues of the leaf, so as to give a more complete 

 illustration of this peculiar structure, even if the leaf in other 

 respects shows many points of likeness to those of various other 

 genera from arid regions such as have been figured and described 

 by Volkens*) and Du val- Jouve. **) Aristida fasciculata is 

 very common on the plains of Colorado, it is perennial and of a 

 caespitose habit; the leaves are rigid, mostly erect, pale-green,. 

 conduplicate when dry and their upper face is deeply furrowed. 

 The cuticle is smooth, but thick, and the epidermis is very thick- 

 walled especially on the lower face where the thickening of the 

 cell-walls is so prominent so as to form longitudinal ridges outside 

 the broad layers of the subepidermal stereome. Short papillae 

 are rather scarce in this species, while numerous, unicellular and 

 pointed hairs abound on the ridges of the upper face of the blade, 

 where they cover the narrow furrows, in the bottom of wliich 

 epidermis is developed as small bands of bulliform cells. The 

 stomata are level with epidermis and are confined to the sides 

 of the furrows. A water-storage tissue of a few layers of large, 

 colorless cells is to be seen underneath the bulliform cells, from 

 where it extends to the subepidermal stereome of the lower surface. 

 The stereome is very thick-walled and accompanies the mestome- 

 bundles as, in transverse sections, broad and flattened groups on 

 both the leptome- and the hadrome-side ; an isolated, smaller group 



*) Volkens, Georg, Die Flora der Aegyptisch- Arabischen Wüpte. 

 Berlin 1887. 



**) Duval-Jouve, G., Histotaxie des feuilles de Gramin^ea. (Annales 

 d. sc. nat. Botanique. Stjries VI. Vol. 1. p. 294.) 



