GROWTH BY THE HOOT. 17 



whole tissue of a plant will therefore become dis- 

 tended with fluid food by the return of spring, and 

 the degree of distension will be in proportion to the 

 mildness and length of the previous winter. As the 

 new shoots of spring are vigorous or feeble in pro- 

 portion to the quantity of food that may be prepared 

 for them, it follows, that the longer the period of 

 rest from growth, the more vigorous the vegetation 

 of a plant will become when once renewed, if that 

 period is not excessively protracted. 



35. Powerful as the absorbing action of roots is 

 found to be, those organs have little or no power of 

 selecting their food ; but they appear, in most cases, 

 to take up whatever is presented to them in a suffi- 

 ciently attenuated form. Their feeding property 

 depends upon the mere hygrometrical force of their 

 tissue, set in action in a peculiar manner by the vital 

 principle ; this force must be supposed to depend 

 upon the action of capillary tubes, of which every 

 part of a vegetable membrane must, of necessity, con- 

 sist, although they are, in all cases, invisible to the 

 eye, even aided by the most powerful microscopes. 

 Whatever matter is presented to such a set of tubes 

 wUl, we must suppose, be attracted through them, 

 provided its molecules are sufficiently minute ; and, 

 as we have no reason to believe that there is, in gene- 

 ral, any difference in the size of the molecules of 

 either gaseous matter or fluids consisting principally 

 of water, it will follow that one form of such matters 

 will be absorbed by the roots of plants as readily as 

 another. Fx)r this reason, plants are pecuharly liable 



