118 



COLLEGE BOTANY 



is the beginning of an elevated line, the raphe, which is formed 

 by the stalk of the ovule. Near the other end of the scar is a 

 minute opening, the micropyle (see page 96). Upon the re- 

 moval of the seed coats we find the embryo or young plant, con- 

 sisting of the two large, fleshy cotyledons or seed leaves, which 

 are attached to a, very short stem, and a plumule or first bud 

 which is the terminal part of the stem. The part of the stem 

 below the cotyledons is known as the hypocotyl and gives rise 



to the radicle or first 

 root, This seed does 

 not contain either 

 nucellus, perisperm 

 or endosperm ( Fig. 



, ,, , 83); they having 



f -==e3B j x^ \^l J been used in feeding 



V 



FIQ. 83. Seed of lima bean; (a, b) showing micro- 

 pyle (mi) and hilum (h); (c) with seed coat and one 

 cotyledon removed showing root (r), hypocotyl (hy) and 

 plumule (pi); (d) germination. 



the growing embryo 

 during the develop- 

 ment of the seed. 

 Therefore, the coty- 

 ledons serve both for the storage of food and as the first leaves 

 of the young plant. 



The embryo is much larger than in most seeds of other types. 

 Other seeds belonging to this type are the pea, peanut, clover, 

 melon, apple, peach, oak, hickory, walnut and cotton. 



Germination of the Bean. In germination, the radicle 

 elongates rapidly, breaks through the seed coats near the hilum 

 and is the first root. The part of the stem below the cotyledons 

 elongates very rapidly and appears above the soil as a loop. The 

 stems straighten and raise the cotyledons above the soil, the seed 

 coats having been pushed off in the soil or soon after the elevation 



