MICROSCOPIC STRUCTURE OF WEED SEEDS 



521 



into which the straight- walled cells at the margin pass; second, 

 circular cells corresponding to the conical hair-cell of barley ; third, 

 exceedingly short, more or less crescent-shaped cells. Near the 

 margins and on the veins, where they alternate with stomata, the 

 cells of wavy outline are elongated; but in other parts they are 

 very short, often being broader than long. Although thick-walled, 

 the walls are transparent, whereas the middle lamella is con- 

 spicuous, giving the impression of thin-walled cells. Pores are few 

 and inconspicuous. Near the margin the circular cells are small 

 and are usually accompanied by crescent-shaped cells which often 

 exceed them in size. On the greater part of the glume, however, 

 the circular cells are much larger, often being 70^ in diameter. 

 Numerous pores are conspicuous, both in the radial and tangential 

 walls. Often one, sometimes two, crescent-shaped cells accompany 

 a circular cell. Characteristic of this coat are the short, wavy 



Fig. 399. Darnel. Middle portion of flowering glume. X 160. 

 (After Winton, Conn. Agr. Exp. Sta.) 



cells and the numerous circular cells, the latter frequently exceed- 

 ing in area the former. 2. Hypoderm. The fibers in this layer 

 are much the same as in cereals. Fibers of similar structure also 

 make up the ground-tissue of the awn. 3. Spongy -Parenchyma. 

 The elements are more or less rectangular in shape, like those of 

 the corresponding layer of barley, and are readily distinguished 

 from the star-shaped elements of oats. 4. Inner Epidermis. This 

 layer is made up of thin-walled cells and stomata, and is of no 

 diagnostic importance. 



