108 A PRIMER OF BIOLOGY 



the latent life of the embryo is awakened and, in the 

 process of germination, it continues the development 

 . v so long interrupted. During 



this resting period, again, the 

 embryo is effectively protected. 

 For example, the seed of the 

 pea-plant comprises a protective 

 shell or testa, enclosing a mas- 

 sive embryo, consisting of an 

 embryonic shoot or plumule, 

 an embryonic root or radicle, 

 and two large swollen "seed- 

 leaves " or cotyledons, filled 

 Popla . with reserve p ro teids and carbo- 

 hydrates (Fig. 51). During germination the insoluble 

 reserves are, by the action of enzymes, transformed 

 into soluble substances, 

 and serve to .nourish 

 the plumule and ra- 

 dicle until the former 

 has developed green 

 leaves above ground, 

 and the latter has 

 obtained a firm hold 

 on the soil and has 

 developed branch roots 

 and root-hairs for ab- 

 sorbing the necessary 

 salts and water. In 

 the case of the castor- 

 oil seed (Fig. 52), the FIG 55 Fruit O f Medicago, 

 reserves chiefly pro- closed and open. 



teid and oil are 



stored wdthin the testa but outside the embryo, 

 which latter appears as a minute nodular body 



