Holm, Some new anatomical characters for certain Gramineae, 105 



of this tissue is also observable on the leaf margin, besides, as 

 stated above, there are layers of stereome underneath the water- 

 storage-tissue between the ribs; it is not unusual to find almost 

 the entire lower face of the leaf covered by one confluent mass 

 of stereome. The mesophyll consists of palisades, which radiate 

 towards the center of the mestome-bundles, and no mesophyll 

 was observed in the furrows. — We have, already, described the 

 sheaths, that are observable around each bündle, but we might 

 State here, that both of these show the same tendency of becoming 

 thick-walled when in contact with the supporting stereome as the 

 ordinary parenchyma-sheath, a fact that is readily observable in 

 the larger bundles. The mestome bundles are all located in the 

 ribs, of which the mediane one is not larger, neither more 

 projecting or thicker, than most of the others; in regard to the 

 ■outline of the bundles, seen in transverse sections, this is mostly 

 oval, very seldom orbicular. 



The occurrence of the double parenchyma-sheatb is not, 

 however, restricted to the leaf, but is also noticeable in the culm, 

 though with the following modification ; it is only present on that 

 part of the mestome-bundles, which is also surrounded by the 

 green cortex, palisades that are arranged in the same manner, 

 as observed in the leaf. But where the mestome-bundles are 

 directly surrounded by stereome, the sheaths are not developed. 



The leaf structure of other species of Aristida.*) 



Aristida fascicidata belongs to the section Chaetaria of 

 Bentham and Hook er, a genus with Beauvais and Nees, 

 and since this section is exceedingly well represented in North 

 America, we have also examined a number of other species to 

 ascertain whether this structural peculiarity is a sectional or only 

 a specific character; moreover we have compared the leaf structure 

 of a few species of the same section, but from other parts of the 

 ^vorld. 



The following species of the section Chaetaria have been 

 «xamined : 



Aristida Adscensionis L. (Eastern India). 



„ arizonica Vas. (New Mexico: Santa Fee). 



„ hasiramea Engelm. {Arizona: Sierra Tucson). 



„ Behriana F. v. Muell. (Australia). 



„ hromoides H. B. K (Texas). 



„ coerulescens Desf. (Spain: Malaga). 



„ delicatida Höchst. (Abyssinia). 



„ depressa Retz. (East India). 



„ dispersa Trin. et Rupr. (New Mexico : Organ Mts.). 



„ fasciculata Torr. (Colorado: Denver). 



*) In securing this exteusive material of Aristida the writer is greatly 

 indebted to Professor Arechavaleta, Messrs. Ths. H. Kearney and F. 

 Lamson-Scribner for specimens of several rare species, which have 

 been of great importance in the present study. 



