MICROSCOPIC STRUCTURE OF WEED SEEDS 



541 



Fig. 417. Microscopic structure of seeds of Mustard family (Cruciferae) . 



I. Hedge Mustard (Sisymbrium canescens) . II. Small Peppergrass (Lepidium 



apetalum). To the right an enlarged epidermal cell with mucilaginous walls. 



ep=epidermis. p=parenchyma. em=embryo. 



(Drawing by L. H. Pammel.) 



their greatest development between the cotyledon and caulicle. 

 First row of cells of embryo nearly isodiametric, filled with oil 

 and protein grains. Others somewhat larger contain the same 

 substances. Cotyledons incumbent. Central part of caulicle sepa- 

 rated from the rest. Cells of caulicle very much larger than cells 

 of cotyledons. 



Black Mustard (Brassica nigra Koch.). 



The cuticle covers the epidermal cells as a continuous layer; 

 when mounted in alcohol the outer layer is very much compressed 

 and shows very slight stratification ; the cell walls expand and 

 after it has been moist for a considerable time the cuticle breaks. 

 Stratification is very evident on the addition of water. The second 

 layer consists of rather thin-walled parenchyma. The cells of 



