3i8 THE STRUCTURE OF ECONOMIC PLANTS 



ANATOMY 



The Seed. — The seeds are somewhat kidney-shaped, i to 3 mm. 

 in length, about twice as long as broad, and the seed coat is rela- 

 tively smooth, varying from a dull yellow, sometimes tinged with 

 green, to a reddish brown. (Fig. 160, B.) Its structure, which 

 has been investigated by Pammel (14), Winton (37), and Lute (18), 

 appears to have a significant relation to the problem of germina- 

 tion. The outermost layer of the coat consists of a row of palisade 



cu 



s c 



end- 



B 



cot- 



^joo&pononmoO^^ 



Fig. 160. A, fruit; B, seed; C, transection of portion of seed coat and cotyledon: cot, 

 cotyledon; cu, cuticle; end, endosperm; ep, epidermis of cotyledon; / /, the light line; 

 pal, palisade cells; par, parenchyma; s c, seed coat; sub ep, sub-epidermal layer of "hour- 

 glass" cells. (/4 and C redrawn after Winton.) 



cells, called Malpighian cells by Pammel, which are from 35 to 

 4x /i high and 8 to 10 ju broad. Their outer ends are rounded, and 

 the exposed surfaces are covered by a thin cuticle which forms a 

 continuous layer of unequal thickness and extends between the 

 conical projections of the palisade cells. (Fig. 160, C.) The 

 "light line" is situated below the cuticle at the upper limits of the 

 palisade layer, and can be readily observed in transections of the 

 seed coat. The lumen of the palisade cell is large at the base and 

 tapers toward the top, being very narrow in the upper part of the 

 cell owing to pronounced thickening of the cell walls. The 

 radiating character of the cavity at the top of the cell can be seen 



