524 



WEED FLORA OF IOWA 



in wheat fields, the fungus is also a common accompaniment. After 

 treatment with potash this layer is stained bright yellow by zinc 

 chloride of iodine. 



Endosperm. — 1. The Aleurone Cells (al) vary from less than 20 

 to 40m in diameter. 2. Starch-Parenchyma (st). The thin-walled 

 cells contain small polygonal grains 3 to 7^ in diameter. The in- 

 dividual starch grains are not distinguishable from the grains of 

 rice and oats, and like the latter, often occur in aggregates of 

 various sizes. 



Fig. 402. Darnel. 



Elements of fruit in surface view. Significance of letters 



same as in Fig. 401. X 160. 

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



URTICACEAE, NETTLE FAMILY. 



Hemp (Cannabis sativa L.). 



The smooth crustaceous achene consists of an outer epidermal 

 layer of thick-walled cells with wavy outline, the thickness of the 

 radial walls varying somewhat. This is followed by a layer of 

 loosely arranged parenchyma cells, and a layer of cells with brown 

 contents. A layer of small cells spoken of as the dwarf cells by 

 Winton, may also be made out in some sections. The palisade 

 layer consists of thick-walled cells with pore canals, the walls 

 having a wavy outline. The cell cavity is very much reduced. 

 The testa is very thin and consists of thin-walled elongated paren- 

 chyma cells, the second layer of spongy parenchyma. The com- 



