MICROSCOPIC STRUCTURE OF WEED SEEDS 545 



ROSACEAE, ROSE FAMILY. 



White Avens (Geum canadense Jacq.). 



A greater part of the so-called seed is made up of the pericarp 

 consisting of a layer of small epidermal cells with trichomes. The 

 underlying parenchyma cells are large with numerous intercellular 

 spaces. The testa is thin, consisting of an outer pigment layer 

 followed by several rows of thick-walled, colorless cells. 



Fig. 419. Microscopic structure of fruit of Avens (Geum canadense). 



ep=epidermis. p=parenchyma. per=pericarp. t=trichome. t 1 =testa. 



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



LEGUMINOSAE,* PULSE FAMILY. 



Rattlebox (Crotalaria sagittalis L.). 



The testa not strongly developed ; endosperm 196a* in thickness. 

 From Nadelmann's studies it appears that in Crotalaria verrucosa 

 the horny endosperm is well developed, being four and one-half 

 times as wide as the testa. The aleurone layer contains fat and 

 aleurone grains. The cells of the embryo contain protein and fat 

 but no starch. 



♦The descriptions here given are taken for the most part from a paper by 

 L,. H. Pammel, Trans. Acad. Sci. St. Louis, 9. 



35 



