MICROSCOPIC STRUCTURE OP WEED SEEDS 



555 



Fig. 423. Microscopic structure of the seed of common Flax (Linum usitatia- 



simum). 

 ep=epidermis. p=parenchyma, underneath thick-walled sclerenchyma cells and 



the pigment layer. pi=pigment layer. en=endosperm. 



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



pigment layer and consists of 2-6 layers of cells, the walls being 

 thicker than those of the embryo, and containing fat and aleurone 

 grains. The epidermal cells of the embryo are squarish, the cells 

 underneath on the upper face of the cotyledon are palisade-like. 

 All of the cells contain fat and protein. 



GERANIACEAE, GERANIUM FAMILY. 



Carolina Cranesbill (Geranium carolinianum L.). 



The testa of the smooth small seeds consists of an outer epider- 

 mal layer, the cell walls not greatly thickened; underlying it 

 is a single row of elongated parenchyma cells followed by the Mal- 

 phigian cells; the light line is narrow and occurs in the middle of 

 the cell; this is followed by a layer of much larger cells with 

 thick walls. The inner seed coat is much compressed and consists 

 of several rows of small cells and a single row of large cells. The 

 walls in both cases are not greatly thickened. The nucellus is 

 much compressed. The cells of the endosperm are not much longer 

 than broad. The cells of the outer row or the aleurone layer are 

 much smaller than those of the second layer. 



