42 GRASSES OF IOWA. 



The bulliform areas are composed of from three to seven 

 rows of polygonal cells with thin walls. They are arranged 

 longitudinally with the leaf and are occasionally interrupted 

 by or grade intD the exserted cells about the base of the large 

 hairs. These areas usually consist of about fourteen rows of 

 epidermal cells. They are located alternately with the veins. 

 The epidermis of the lower or outer face is much the same as 

 above, except that the bulliform cells, hairs, and spur-like 

 hairs or tubercles are wanting, and the walls are thicker. 



Stomata. — The stomata occur in longitudinal rows; the two 

 narrow guardian cells containing chlorophyll are surrounded 

 by two large secondary cells. A thin cross-section of leaf of 

 Sporobohfs heterolepis shows a nearly continuous row of rec- 

 tangular epidermal cells, broken only by the stomata. 



The ecological parts of the grass leaf are rather instructive. 

 The cuticle and cell walls are strongly developed in the corn. 

 The same is true of many other dry climate grasses. In 

 grasses like barnyard grass, the epidermal cells are larger and 

 the cell walls and cuticle less developed, as they grow in 

 placEs where moisture is obtained easier and transpiration is 

 not so excessive. The chlorophyll-bearing parenchyma sur- 

 rounds the bundles and diifers somewhat in different genera. 

 In Sporobolus heterolepis large parenchyma cells surround the 

 bundles. These are joined by one or more rows of smaller 

 cells to the outside. In this arrangement there is economy, 

 since the plant can carry away the elaborated food materials. 

 The blades as well as sheath are frequently provided with tri- 

 chomes, abundantly produced in Bromus mollis, Leersia oryzoides, 

 Zea (Mexican corn). Those interested in a further study of 

 the anatomy of leaves should consult specially the works of 

 Hackel, Holm, Miss Emma Sirrine, Miss Emma Pammel, 

 Duval Jouve, Ball, Combs and others. These studies are of 

 value from a systematic standpoint, as has been abundantly 

 shown by Holm, Jouve, Ball and others. The character of 

 bundles, sclerenchyma, bulliform cells vary in different genera 

 and species, and often may be used to determine the species 

 and help to separate them, but we should not lose sight of the 

 fact that allied species present somewhat similar characters 

 and usually have a similar structure. 



