354 The Living Plant 



definite places, resulting in outgrowths which wax greater and 

 greater until they become the thick leaves that later are called 

 the cotyledons. Meanwhile the original ball is growing more 

 actively at the opposite end, there producing a cylindrical struc- 

 ture which forms the stem, or 

 hypocotyl, of the embryo, while 

 a group of growth cells at its 

 tip forms the foundation for 

 the forth-coming root, and 

 , another between the cotyle- 



I-IG. 13o. Typical seeds, with embryos, of 



the two leading types; "albuminous" (a dons forms the foundation for 



Barberry) and " exalbuminous " (an Apple) , , ~ . i i j mi 



as further explained in the text. (Copied the .IlTSt terminal DUQ. 1 hUS 



are the first leaves and stem, 



and the foundations for the first root and bud, of the new 

 plant laid down wholly inside the embryo-sac of the ovule, 

 forming the structure which we call the embryo. Simultaneously 

 the coats of the ovule are growing thicker and harder, the suspen- 

 sor is being absorbed, and a supply of food substance, the endo- 

 sperm, developed in a manner already described (page 299), is 

 filling all the space in the embryo-sac not preoccupied by the 

 embryo. The resultant structure, a combination of embryo, food 

 substance, and protective coats, is the Seed (figure 135, on the 

 left). 



Such is the typical method of development of embryos and 

 seeds, though of course a great many differences occur in detail. 

 In some seeds the development stops at the point here described, 

 leaving the young embryo surrounded by copious endosperm or 

 "albumen"; but in others, for example, Peas and Beans, the 

 embryo continues its development until it has absorbed all the en- 

 dosperm and everything else inside of the seed coats, in which case 

 it usually develops also the first bud, called the plumule, between 

 the cotyledons (figure 135, right). In any case, the seed is now 

 ripe. It gives up most of its water, hardens its coats, separates 

 from the parent plant, and goes into that resting state, in which 



