of sinuosity through the whole stomatal 

 zone. 

 Sinuosities very irregular, stomata very broad 

 (about 35 microns) crown cells present 



wheat 



Sinuosities regular, crown cells absent. 

 Stomata with average width of about 50 



microns barlev 



Stomata wider, average width of about 50 



microns ry ? 



ft. Epidermal cells with straight, thick and only sligh 1 

 ly undulating walls, or straight 



epidermis of internod>' 



Crown cells present, stomata very wide (31 



microns) wheat 



Crown cells absent. 



Wall straight oat 



Walls slightly undulating. 



Cells 15 — 18 microns wide, walls very slight];* 



undulating, stomata small barle.v 



Cells 18—22 microns wide, walls slightly un 



dulating, stomata large rye 



It must be admitted to be difficult to apply the above 

 • riteria, but they seem to be the only ones available 

 It is more difficult to distinguish rye and barley, if 

 one makes use only of the above marks, though easv 

 lo separate them from oat and wheat. The following 

 paragraphs will however show that rye and barley ar<; 

 easily separable by other characters. 



The preceding description of the epidermis does, not 

 include the epidermis of the inner face of the leal 

 sheath, that namely which lies in contact with the sur 



face of the stem (internode). Although in most re 

 gards the structure is very uniform in all the straw h 

 there are certain differences which stand out pro- 

 minently. In general, the walls of the long cells are 

 very thin and straight, there being no suggestion of 

 undulations, and they are very similar to each other 

 in all the kinds of straw. The stomata and the dwarf 

 cells however are distinctive. 



The dwarf cells in wheat and rye are for the most 

 part in the form of minute trichomes (figures 29 e-f). 

 They are three or four times as numerous in rye than 

 in wheat, and are so small that it requires either mi- 

 croscopic observation, or a sense of touch equal to that 

 of the tip of the tongue to detect them. For this reason 

 the latter method has been indicated in a previously 

 given key. They are absent from the oat. 



The stomata in rye and wheat (figure 29, c, d) are 

 similar in that the guard cells taken together, are as 

 broad as the long cells where tJhey articulate with the 

 guard cells, while in the oat and barley (figure 29, 

 a, b) they are usually much narrower. In barley the 

 fore-pore (the vestibule, or outer entrance) is small 

 and well marked, while in oat it is not. Summarizing 

 in the form of a key we have a 



Key based on the characters of the inner epidermis of 

 the leaf sheath. 



A. Guard cells as wide as long cells. Minute trichomes 

 present : 



Stomata large (60—70 microns long) .. ..wheat 

 Stomata small (about 50 microns long) . . . rye 



B. Long cells wider than the guard cells; no trichomes 

 in oat. 



Figures 30-33. 



Maceration products of barley, oat, rye 

 and wheat resp. x 23. 



