CHAPTER IX 



SEEDS AND SEEDLINGS; SEED DISTRIBUTION 



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

 si'ed has ah-eady 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.i The most important parts of 

 ordinary seeds are : 



(1) The enihryo, or miniature plant. 



(2) The plant food stored elsewhere than 

 m 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 

 seeds of the various 

 groups into which or- 

 dinary seed plants are 

 assembled on account 

 of their relationship to 

 each other. Many em- 

 bryos show a fairly 

 well-defined set of or- 

 gans, — the hypocotyl, 

 or little stem ; the coty- 

 ledons, or seed leaves ; 

 and the plumule, or 

 seed bud. 



hi 



Fig. 125. Length- 

 wise section of 

 squasl] 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- 

 dosperm ; t, testa. 

 Two and one-half 

 times natural size 



Fig. 126. A common bean 



split open, after soaking 



in water 



h, hypoeotyl, lying on one of 

 the cotyledons ; g, groove in 

 the other cotyledon where 

 thehypocotyl lay ; p, plumule 



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

 New York. 



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

 perigperm. 



136 



