CHAPTER IX 



\--e 



SEEDS AND SEEDLINGS; SEED DISTRIBUTION 



126. Gross structure of seeds. The definition of the term 

 seed has already been given (Sect. 22). The structure of seeds 

 varies so greatly in details that in this place it 

 will be possible to describe only a very few 

 typical forms. 1 The most important parts of 

 ordinary seeds are : 



(1) The embryo, or miniature plant. 



(2) The plant food stored elsewhere than 

 in the embryo, usually known as endosperm? 



(3) The seed coat or coats. 



All of these parts are well shown in Figs. 

 125 and 126. The embryo differs greatly in 

 P seeds of the various 



groups into which or- 

 dinary seed plants are 

 assembled on account 



FIG. 125. Length- of tn eir relationship to 



wise section of each other. Many em- 

 bryos show a fairly 

 well-defined set of or- 

 gans, the hypocotyl, 

 orli 

 ledons, or seed leaves ; 



] -hyp 



squash seed 



hi, hilum, or scar, 

 marking place of 

 attachment to the 

 ovary ; hyp, hypo- 

 cotyl ; p, plumule ; 

 c, cotyledon ; e (in- 

 nermost layer next 

 to cotyledon), en- 



FIG. 126. A common bean 



stem ; the coty- split ope ^ soakin " 



h, hypocotyl, lying on one of 



dosperm ; t, testa. and the plumule, or the cotyledons ; g, groove in 

 Two and one-half n ' * the other cotyledon where 



times natural size seed bud. 



the hypocotyl lay ; p, plumule 



1 See also Gray, Structural Botany, chap. viii. American Book Company, 

 New York. 



2 When this reserve food is formed outside of the embryo sac it is called 

 perisperm. 



186 



