206 Trans. Acad. Sci. of St. Louis. 



are elongated, thick-walled, with a small lumen. The aleurone 

 cells are nearly as long as broad, densely filled with protein 

 grains. The cells of the starch layer are much larger than in 

 the aleurone, and densely filled with compound starch grains. 

 The individual components are more or less angular owing 

 to pressure. The compound grains are not nearly so large as 

 in Avena and Zizania. The grains contain from two to a 

 dozen component parts. The embryo contains a blackish- 

 blue pigment (PI. XVIII. 8). 



Stipa, L. The genus Stipa has been studied by Harz l 

 and Zimmermann, 2 also in a very general way by Darwin. 3 



Stipa robusta, Scribner. The outer part of the caryopsis 

 consists of rather thick-walled tangentially elongated cells. 

 The surface of the nearly colorless epidermal cells is slightly 

 uneven, having somewhat the appearance of little circular rings. 

 The underlying three or four rows of cells are very much com- 

 pressed. They are likewise colorless. The cells are tangen- 

 tially alongated. The testa is dark in color and consists of 

 two differentiated layers. In a cross section, the outer row 

 is seen to consist of small thick-walled cells. Minute longi- 

 tudinal canals are evident, with a very narrow cell cavity; 

 tangentially these cells are elongated, slightly curved, with 

 prominent cross striae. The layers below are much com- 

 pressed and consist of tangentially elongated cells, brown in 

 color. Harz states that remnants of the nucellus remain in 

 sStipa pennata. The aleurone layer consists of a single row 

 of cells somewhat longer than broad. The remaining por- 

 tion of the endosperm consists of starch cells somewhat 

 variable in size, densely filled with small simple grains. 

 The individual elements are angular because of pressure. 

 Stipa pennata according to Harz has both simple and com- 

 pound grains. If the grains of S. robusta are compound, the 

 component parts are easily separated. The adherent glume 

 consists of thick-walled sclerotic elements with pore canals, 

 in longitudinal view elongated, tapering at both ends (PI. 

 XVII. 13). 



1 1. c. 1282. 2 1. c. 



s On the hygroscopic mechanism by which certain seeds are enabled to 

 bury themselves. Jour. Linn. Soc. 1: 151-167. pi. 23. 



