30 



GRASSES OF IOWA. 



and in many respects similar to the species described above. 

 The stereome of the superior face is widely separated from 

 the mestome bundles by the parenchyma. In Pleuropogon cali- 

 fornicum there is a distinct mestome sheath surrounding the 

 bundles and the walls are thick. The leptome and hadrome 

 are separated from each other by two layers of thick- walled 



parenchyma cells. In the large bundles stereome occurs 

 above and below. They are separated from the parenchyma 

 sheath by a few colorless cells. It may be interesting to 

 compare the leaf structure of xerophytic and mesophytic 



