22 BOTANY 



when a drop of water will ooze out of it. On removing 

 the testa the body of the seed is found to consist of 

 a very bulky embryo. The two cotyledons are large 

 masses placed face to face and easily separated from 

 each other. On gently moving them apart each is found 

 to be attached to a very short axis which lies between 

 them and is almost hidden when their faces are in con- 

 tact. The lower end of the axis is the radicle and is 

 bluntly pointed ; the upper end, the plumule, which curls 

 inwards between the cotyledons, bears two minute leaves. 



We may compare with the bean a seed of about the 

 same size, that of the castor oil plant. It must be 

 soaked until it swells, when the hard coat it possesses 

 will crack. On removing the latter a fleshy mass will 

 be seen which cannot be separated into two portions 

 without splitting it. If it is divided into two it will be 

 iound that the embryo plant consists of two very thin 

 flat cotyledons lying in the centre face to face, with the 

 very short axis (plumule and radicle) between them. 

 The fleshy part of the seed surrounds the whole and 

 adheres firmly to the backs of the delicate cotyledons. 

 This mass is the endosperm, which has not been absorbed 

 by the embryo during its early growth. 



If the seed is soaked in alcohol this dissection is easier, 

 as the parts do not then adhere so closely together. 



After a period of variable length the embryo awakes 

 from its quiescent or resting state and develops into a 

 seedling, which goes on to become an adult plant. The 

 quickening into this renewed activity, which is techni- 

 cally called its germination, is only possible when the 

 external conditions become favourable. The process 

 demands moisture, a moderate degree of warmth, and 

 the presence of oxygen. It may be studied easily with 

 a little care, as it can take place in an ordinary room. 

 The -absence of light is not essential, although seeds are 

 usually buried in the soil before they germinate. 



