THE FRUIT 123 



embryo absorbs the contents of the cells of the endo- 

 sperm and so fills the embryo sac. In others, as in the 

 castor oil seed, a good deal of endosperm remains ; in 

 yet others part of the ovule may have escaped absorp- 

 tion by the growing embryo sac. In all cases there soon 

 comes a period when the growth and development of all 

 these parts stops and the resulting structure, now 

 become the seed, enters on a more or less prolonged 

 period of absolute rest. This is the period during which 

 alone the migration of the species is possible, as by 

 various means the seed is carried from the parent plant. 



We called attention at the outset to the fact that the 

 life of the individual plant has to be spent absolutely in 

 one spot, that at which it is rooted to the ground. How 

 disadvantageous this is to the plant and what an endless 

 series of struggles against the difficulties it involves, has 

 been one of the principal lines of thought throughout 

 our study. The final difficulty meets us when we con- 

 sider the production of offspring. How can they 

 possibly flourish or even survive when their parent is 

 hampered in this way ? The solution of the difficulty is 

 found in the provision which is made for the wider dis- 

 persal of the reproductive bodies, mainly seeds. 



The fact that most plants produce many seeds and 

 that each seed after a period of rest produces a new 

 plant makes it imperative that adequate means of dis- 

 persing seeds shall be found, or clearly the problem of 

 the maintenance of the species would not be solved. 

 We must turn, therefore, to consider this matter closely 

 and to study certain new structures which are immedi- 

 ately concerned with it. 



The migration of seeds is brought about in an almost 

 infinite variety of ways, each species having its own 

 mechanism. In most cases it is associated with the 

 development of a new structure, the fruit. 



While the changes are taking place by which the 



