GERMINATION. 75 



that light was thrown upon them from below upwards, 

 they then sent their radicles upwards, and plumula 

 downwards. 



25. Though it is the general rule that the radicle 

 tends towards the centre of the earth, an exception may 

 be found in the parasitical plant, the Miseltoe, in which 

 the radicle obeys the attraction of the body upon which 

 it germinates. 



26. With this lengthening of the radicle and direc- 

 tion of it beneath the earth, and the elevation of the 

 cotyledons above it, which become green by the fixation 

 of carbon within their tissue, the plumula becomes 

 more and more evolved in consequence of the exciting 

 action of the nutritious matter already absorbed by the 

 radicle, (though in some cases it is much dependent 

 upon the raised cotyledons,) and becomes at length ex- 

 panded into the perfect leaf, after which the cotyledons 

 soon cease to exist. 



27. The plumula, like the radicle, has an equally 

 strong tendency to a particular direction, and which is 

 equally unalterable, its direction being upwards to the 

 light. From the experiments of Schultz we perhaps 

 may conclude that light is the object which the radicle 

 endeavours to avoid, and so causes its direction down- 

 wards, whilst it is that which the plumula seeks, and so 

 gives rise to its tendency upwards ; but whatever may 

 be the cause, the primary tendency exists in the embryo 

 portions as a true and determinate vital action, subject 

 in its proximate causes to a power strictly of vitality, 

 though its more ultimate ones may be looked for else- 

 where. 



28. We have now the young plant so far deve- 

 loped ; the descending axis is carrying on its office of 

 procuring material for still further development, and 

 the expanded plumula is also performing its functions ; 

 all further progress being dependent upon the due per- 

 formance of the process of nutrition, which operation 

 we shall now consider. 



