106 



A PRIMER OF BIOLOGY 



plants, which, in many cases, measure their duration 

 by centuries. During these periods, annually or 



more frequently in 

 the year, or at 

 intervals of two or 

 more years, repro- 

 ductive cells are 

 formed and off- 

 spring are pro- 

 duced. 



In order that the 

 offspring may have 

 a chance in the 

 struggle for exist- 

 ence it is manifest 

 that they must not 

 only be protected 

 during the early 

 stages of their ex- 

 istence, but also 



that some provision must be made for their proper 

 nourishment during the embryonic 

 period and until they are capable 

 Protection of feeding themselves. Both these 

 necessities are provided for in a 

 variety of ways. 



The lower the rank of the 

 organism the less provision is 

 made for it in either respect. In 

 the very lowest forms, indeed, no FIG. 52. Seed of Cas- 

 provision at all is made, and the tor-oil = , testa ; 6, 

 offspring, newly born, are left to 

 shift for themselves and take their 

 chance among the favourable or unfavourable con- 

 ditions of the environment. But higher up the 



FIG. 51. Two stages in the germina- 

 tion of a bean. In A the radicle has 

 developed and the plumule is on the 

 point of escaping from the testa ; in 

 B the plumule is beginning to unfold. 



and 

 nourish- 

 ment of 

 embryos. 



food reserve ; c, cot- 

 yledon ; d, radicle. 



