1908] HOLM—ALPINE GRAMINEAE 435 
larger (oval) and smaller (orbicular) ones; and hypodermal stereome 
occurs outside each of the mestome strands, but is only in contact 
with the leptome side of the larger ones; the smaller strands only 
touch the inner stereome with their hadrome side. When two con- 
centric bands of mestome bundles occur, the peripheral ones are the 
smallest and are orbicular in cross-section; the inner ones are either 
e - 
Diagram showing the structure of the culms of Agrostis canina var. (A), Poa 
Lettermanni (B), P. rupicola (C), P. alpina (D), and Agropyrum violaceum (£). 
Orbicular (D) or oval, often representing two sizes, as shown in E. 
Nn these culms (D and E) the stereome shows two well-marked 
Modifications. It constitutes a mechanical support on the leptome 
Side of all the mestome strands in D; while in E this hypodermal 
Support is confined to the peripheral strands alone—those of the 
inner band (E) are imbedded in a zone of stereome, which does not 
€xtend to epidermis. The structure illustrated by E was observed 
In_ Calamagrostis purpurascens, Agropyrum violaceum, and Des- 
champsia caespitosa from Graymont; while D is the most frequent 
