examined, (figure 5), it will be seen at once that the 

 appearance offered by, the transverse section gives a 

 totally inadequate conception of the shapes of the con- 

 stituent cells, many important details not appearing at 

 all, especially in such small objects as the grass stem, 

 the total thickness of which is 0.5 mm. or less in thick- 

 ness. However, by means of maceration (in chromic 

 acid for example) the cells may be set free from each 

 other and thus examined. With the additional help of 

 this method we may examine each tissue in turn begin- 

 ning with the epidermis. 



THE EPIDERMIS Figures 6-13). 



Examined en face the epidermis is seen, in general, 

 to be composed of longitudinal zones of more or less 

 elongated cells with undulating walls overlying the 

 green tissues beneath, alternating with narrower zones 

 of similar but longer cells with straight walls, and with 

 narrower lumina. 



The long cells are interrupted frequently by the so- 

 called "dwarf-cells", which occur usually in pairs 

 placed longitudinally, but may be either single, in threes 

 or in fours. Of the pair, one cell is thin-walled and 

 stains readily in the manner of the epidermal cells in 

 general. This, Avhen there is but one dwarf-cell in a 

 position, is the cell wliich may assume the form of a 

 trichome usually shaped like a cat's claw. The other is 

 thicker walled, usually, and the walls are strongly sili- 

 cified. Wiesner (1900) states that this is the case and 

 Hoehner (through Haberlandt. 1909, p. 105) represents 

 them as single. Only one of the pair however, presents 

 this character. The representation by Hoehnel seems 

 to be referable to the circumstance that sometimes the 



il s g '/>v>' i v ?% si . at 



cells in question are very small and sheared upon each 

 other so that they can be resolved microscopically only 

 in depth and not transversely (figure 14). In barley 

 especially they are very small and difficult to resolve. 

 In wheat however the silicified cell may be quite large 

 relatively. 



The long cells of the epidermis are interrupted also 

 by groups of four cells forming the stomata. These 

 are organs which are capable of forming openings 

 through which gasses can pass into and out of the 

 stem (figures 29a-d ; 15). The four constituent cells 

 are arranged in the grasses in a transverse row. The 

 two adjacent ones, the "guard cells", are slender, and 

 have a slit between them which opens and closes in life 

 according to physiological conditions. The outer two 

 cells are the accessory cells. The relations are best un- 

 derstood by examining a transverse section (figure 15). 



Epidermis of the stem. The epidermis of the stem 

 and of the leaf both present similar fundamental feat- 

 ures as just described. They are, however, sufficiently 

 different in details as to demand separate examination 

 (figures 6-9). 



It is practically impossible to fit a single description 

 to the epidermis -of the stem for the reason that it shows 

 marked differences in different portions of the inter- 

 node. In the lower portion, the cell walls (in wheat, 

 e.g.) are quite straight and thin, the dAvarf cells are 

 longer and very simple in structure. The stomata are 

 few in number and less differentiated. In the upper 

 portion, on the other hand, especially where the inter- 

 node is not covered by the leaf-sheath, the cells have 

 walls which are thick and undulating, and they occur 

 in longitudinal zones alternating with zones of ceDs 

 with straight walls. The dwarf cells are here strongly 



I IT/ MO UM 



Figures 10-13. — The epidermis viewed en face of the lower (outer) surface of the leaf sheath of barley, oat, rye and 



wheat resp. X 170, 



