l8 9i] Anatomical Characters of N. Am. Graminetz. 277 



rough epidermis of the superior face of the blade, where 

 numerous thorn-shaped expansions are intermixed with coni- 

 cal warts. The stereome is rather strongly developed, while 

 the mestome-bundles, the mesophyll, etc., agree with what 

 has been mentioned above for the typical form. 



D. maritima Raf. , var. laxa, $ from Utah: The epidermis 

 of the leaf is nearly smooth on both faces, being destitute of 

 hairs and thorn-shaped expansions ; otherwise it agrees per- 

 fectly with the preceding variety. 



D. thalassica Humb. et Kth., $ from Lower California : 

 The leaf of this species shows the same structure in most 

 details as the preceding D. maritima. It is, however, quite 

 well characterized by the very rough epidermis, of which that 

 of the superior face shows several sharp-pointed expansions, 

 while that of the inferior face has numerous conical warts. 

 The largest mestome-bundles have a closed ring of thick- 

 walled parenchyma inside the proper sheath, and the leptome 

 contains groups of similar cells, by which it is also separated 

 from the hadrome. The stereome represents groups of con- 

 siderable size above and below the largest mestome-bundles, 

 but is entirely wanting below the smallest ones. 



D. prostrata Benth., <5 from Mexico: The leaves are rough 

 above, hairy below and along the margins ; the epidermal 

 expansions of the superior face are thorn-shaped, while those 

 of the inferior are merely warts or soft hairs. The mestome- 

 parenchyma does not show such thick-walled cells as described 

 for the preceding species, and the leptome is but imperfectly 

 separated from the hadrome. As to the stereome, this forms 

 merely small groups above and below the strongest mestome- 

 bundles, and the uncolored parenchyma is only represented by 

 small groups between the bulliform cells and the inferior epi- 

 dermis. Considered altogether the anatomical structure of the 

 leaf in the genus Distichlis is very uniform, and it does not 

 seem possible to give any special characters, by which either 

 the varieties or the supposed species thalassica and prostrata 

 may be distinguished from the species maritima ; because we 

 have seen that male and female specimens of this last show 

 variations among themselves nearly equivalent with the differ- 

 ences in the two varieties and subspecies. 



Of the genus Pleuropogon, which is closely related to 

 Uniola and Distichlis, three species are known. Two of these 

 P. refractum Gr. and P. Californiawi (Nees), are inhabitants ot 



