MICROSCOPIC STRUCTURE OF WEED SEEDS 



577 



Fig. 439A. Miscroscopic structure of some weeds of the Sunflower family 



(Compositae). 

 I. Small Ragweed (Ambrosia artemisiaefolia). II. Verbesina (Verbesina hel- 

 ianthoides). III. Spanish Needle (Bidens discoidea). IV. Burdock 

 (Arctium lappa). 

 ep=epidermis. scl=sclerotic parenchyma. t=testa. n=nucellus. en=endosperm. 

 em=embryo. pal=palisade cells. 



(Drawings by L. H. Pammel and Charlotte M. King.) 



The pigment layer is followed by elongated sclerotic parenchyma 

 with a narrow cell cavity; cells with granular contents. The testa 

 is thin, cells elongated, cell wall thickened slightly, tinged with 

 yellow. The testa is followed by remnants of the nucellus. The 

 parenchyma cells of embryo follow the nucellus. 



Wood or Field Thistle (Cirsium discolor (Mnhl.) Spreng.). 



The microscopic structure of the yellowish gray seeds shows a 



clear relationship to Arctium; the outer epidermal layer of the 



pericarp consists of thick-walled colorless cells, the walls bright 



and lustrous; the pigment layer underneath the walls, not nearly 



37 



