112 Botanisches Centralblatt. — Beiheft 2, 



^eauvais' Äristida is, on his own grounds, inseparable from 

 the other members of Arthratherum, as Nees also considered it 

 to be. Nees does not even refer to this special iigure of Äristida 

 -lanata Forsk., althou^h he cites the others. 



In bringing these facts together, the anatomical characterization 

 and the systematic position of the species of Äristida, the follo- 

 wing characters have been observed as the most important: 

 yiChaetaria, Curtopogon and Streptacline possess the double paren- 

 chyma-sheath, while most of the species of Arthratherum, those 

 with plumose awns lack it. It is present in the three North 

 American species : A. Californica, A. desmantha and A. tuherculosa, 

 which-otherwige are closaly related to the section Arthratherum, 

 since their awns are articulated and deciduous, even if they are 

 not plumose." 



Allies oi Äristida. 



According to Bentham and Hook er the genus Äristida 

 loelongs to the tribe Agrostideae'^ and is refered to a subtribe 

 y^Sti^jeae"' of which Stijja is typical, and we must therefore look 

 into Stipa and some of the other members of the Stipeae: Ory- 

 zopsis, Eriocoma, ISassella, Piptochaetium, Muhlenhergia and Lycurus 

 as near allies of Aristda. Let us look into the anatoray and 

 Classification of some of these and naturally first of all : 



Stipa L. 



This genus exhibits much the same diversity in the structure 

 of the awn (arista) as we have described above as being charac- 

 teristic of Äristida and its sections: This organ occurs also in 

 Stipa as continuous and persisting or as articulated and deciduous. 

 Moreover the base of the awn is often twisted and of a consi- 

 derable length, while the apex is either naked or distinctly plu- 

 mose, but always entire, never trifid in any of the species of 

 Stipa. 



Aristella Bertol., Streptachne R. Er. and Jarava Ruiz et Par. 

 are some of the genera, which were formerly suggested as segre- 

 gates of Stipa. The species are usually inhabitants of high plateaus. 

 savannas and rocky soil. Some of these are frequently associated with 

 various representatives of Äristida. We had, therefore, expected 

 that at least some of the species of Stipa, and especially those 

 A\'hich possess a naked awn, would have shown the same struc- 

 tural peculiarity, which we noticed in the corresponding species 

 of Äristida namel}' the presence of a double parenchyma-sheath 

 around the mestome-bundles; but as will be shown in the follo- 

 wing pages this structure seems to be possessed by Äristida alone. 



We have examined the leaf-structure of following species: 



Stipa avenacea L. (^Rocks on the Potomac-shore, Maryland). 

 „ capillata L. (Meadows, Nercynsk, Davuria). 

 „ Charruana Arech. (clayish soil, Montevideo, Uruguay), 

 „ comata Tr. et Rupr. (Plains, Denver, Colorado). 

 „ ßlictdmis Arech. (dry, stony plateaus, Montevideo, 

 Uruguay). 



