GENERAL PRINCIPLES. 



Section 8. — The Seed. 



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The perfect seed contains the rudiment of a plant of 

 the same nature as that which produced it. This rudi- 

 ment of the new plant is called the embryo^ and is found 

 in a more or less developed state in all seeds. In fig. 56 

 is given an enlarged view of an apple seed cut longitu- 

 dinally to show the embryo in plnce, and fig. 57 shows 

 the embryo of the same after germination, the lettering 

 referring to the same parts in both illusti'ations. It consists 

 f^"'^^ ^jjjfs. of three parts — the cotyledons (a, 



v^ ^^^.J rlj i figs- ^^ ^'^'^ ^'^)i which are the first 

 ^^^liif pair of leaves, usually rudimentary ; 



these are the parts that first make 

 their appearance, and are known as 

 seed leaves. The bases of these 

 cotyledons are united to the radicle^ 

 (c), and between them is a bud (J), 

 called the plumule. The radicle 

 and plumule are very inconspicuous 

 in the seed (fig. 56), but as soon as 

 the seed is excited into germina- 

 tion by the heat and moisture of 

 the earth, the radicle elongates, one 

 end penetrates the soil, and roots 

 soon start from it, and the upper 

 portion ascends in an opposite direction, bearing the 

 plumule, and, in the apple, etc., the cotyledons to the sur- 

 face, where they find the necessary air and light. The 

 plumule, which is really a terminal bud, is soon lifted up 

 b)"^ the development of a section of stem, unfolds its leaves, 

 and exposing another bud, which in its turn repeats the 

 same process, and thus the growth of the tree goes for- 

 ward. 



It has been remarked tliat a seed contains the rudiments 

 of a plant similar to that on which it is produced; but 



Fig. 56, apple seed divided: 



Fig. 57, germinating seed. 



a, cotyledons ; 6, plumule ; 



c, radicle. 



