GRASSES OF IOWA. 37 



such as belong to the typas of plants kcown as halophytic, 

 xerophytic, and mesophytic. Of the fourth type, hydrophytic, 

 the genus Leersia is good representative, especially Leersia 

 oryzoides which has been well described by Mr. Holm.* In 

 this species the mestome bundles are of three types. A thick- 

 walled mestome sheath, in connection with a layer of thick- 

 walled parenchyma, separate the leptome from the hadrome. 

 Leptome and hadrome are well developed. The largest 

 bundles are not so numerous as the smaller ones of the second 

 degree; in the latter a distinct mestome sheath occurs inside 

 of the colorless parenchyma. The thick-walled parenchyma 

 between leptome and hadrome is absent. The smaller type of 

 bundles contain only leptome with a distinct mestome sheath. 

 Mr. Holm further remarks that in addition to these forms 

 of bundles, which lie in the same plain, there are from one to 

 three very small ones which belong to the upper face of the 

 mid-nerve and this is peculiar to the genus Leersia. 



Epidermis. — The epidermal cells are quite irregular, vary- 

 ing greatly in size. For the purpose of this description it 

 will be convenient to take up the epidermal cells under two 

 headings. First, the general character of cell. Secondly, 

 the buUiform. We miy obtain an idea of the diversity of the 

 structure by a coasideration of some of the different species. 

 One type is very well represented in Bromus inermis. f 



Here the epidermal cells are large, regular and well-devel- 

 oped, with a thick cuticle. The cuticle is thicker below and 

 above the mestone bundles than elsewhere. Trichomes are 

 absent. Stomata occur on both surfaces of the leaf, but 

 especially between the bulliform cells. 



In Festuca tenella, according to Mrs. Hansen,;}; the epidermal 

 cells covering the stereome are thick- walled and not as large as 

 the other epidermal cells. In Andropogon nutans^ the epi- 

 dermal cells are very large, and nearly equal in diameter. 

 The cuticle is strongly developed with hair-like projections, 

 more abundant on the lower than on the upper surface. 



Mr. C. R. Ball has described the epidermal cells of Era- 

 grostis pectinacea, as having thicker-walled cells than in Era - 

 grostis purshii\\ the latter being a species adapted to a dry and 



* A stud V of some anatomical characters of North American Gramlneae. IV. Bot. 

 Gazette. 17:358. pl.^l. 



+ Emma Sirrlne. 1. c. 122. 



* Emma Pammel, 1. c. 129. pi. 9. f. 2. pi. 10, f. 5 and 6. 

 § 0. B. Weaver, 1. c. 133. pi. 12. f. 1 and 5. pi. 15 f. 14. 

 n. c. 141. pi. 16. f. 2. pi. 18. f. 15-16. 



