576 



WEED FLORA OF IOWA 



thinner-walled parenchyma cells. The outer layer of the testa 

 is composed of nearly isodiametric ceUs, followed by larger thick- 

 walled parenchyma cells ; cells of the lower portion compressed. The 

 endosperm is much reduced, of elongated cells; embryo with row 

 of outer cells longer than broad. 



Fig. 439A Fig. 439 B 



Fig. 439. Sunflower (.Helianthus annuua). 



A. Cross section of outer layers of pericarp, o, epicarp with h, hairs ; K, 

 hypoderm ; H, fiber bundles separated by m, parenchyma ; p, parenchyma 

 with g, fibro-vascular bundles. X 160. 



B. Epicarp with h, twin hairs, in surface view. 



After Wlnton. 



Burdock {Arctium lappa L.). 



The brownish mottled fruits consist of a thick-walled pericarp, 

 the outer epidermal layer of thick-walled cells, walls colorless or 

 but slightly colored; the underlying layer of six or eight rows of 

 thick-walled cells, not as thick, however, as the epidermal cells. 

 The first layer carries the brownish or blackish brown pigment. 



