MICROSCOPIC STRUCTURE OF WEED SEEDS 539 



Prickly Poppy (Argemone intermedia Sweet). 



The blackish pitted seeds are difficult to study. They consist 

 of nearly colorless epidermal cells, with thick outer walls and 

 cuticle. The cells of the underlying layer are thick-walled, walls 

 and contents blackish, difficult to make out on account of dense 



Fig. 416. Rocky Mountain Poppy (Argemone intermedia). 

 ep=epidermis with thick outer walls. pi=pigment layer, n=nucellus, en=en- 



do.sperm. 

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



pigment. The nucellus is compressed, colorless. The endosperm 

 of large cells contains oil in large amounts, and protein. The 

 structure seems to differ in a marked degree from Papaver as 

 described by Harz and G. Kraus. 



CRUCIFERAE, MUSTARD FAMILY. 

 Virginia Peppergrass (Lepidium virginicum L.). 



The seed coats consist of three well denned layers. The outer 

 or epidermal cells are tabulated, somewhat compressed. The cuticle 

 forms a continuous layer over these. On the addition of water the 

 epidermal cells elongate and form a mucilaginous mass, showing 

 stratified layers. These are not difficult to make out when the 

 specimen is mounted in water. The cell cavity is very much re- 

 duced ; that portion of the cell wall in contact with the cell cavity 

 is differentiated from the outer cell wall substance. Long con- 

 tinued addition of water causes the cuticle to break and the exterior 

 becomes very irregular. 



The second layer is colored brown, the cell walls are considerably 

 thickened laterally and project upwardly in the shape of cones. 

 A section made through the ends of these seeds shows that the 

 second layer is considerably more developed and there are evidences 



