106 UPWAED GROWTH OF THE HEAD, AJsH pt. ii. 



general directioii it caii find light ; and that the growth below 



groA\'th of ^ ^ 



root to is in whatever direction it can find the best soil. I 



wherever 



goors^iif except the growth of the first tap-root of the seedling, 

 and of its first gemmule, as long as this is below the 

 earth, and consequently not exposed to light. 



The fact shown us by Knight's most beautiful 

 experiment, much as it says, says no more in favour of 

 gravity, or weight, as the director of the growth of 

 plants, than the fact which we see every day, that plants 

 are drawn by light, says in favour of light. 



Fools will rusli in where angels fear to tread ; 



and we may have plenty of them to settle these ques- 

 tions for us nicely. But can the philosophic, or the 

 unphilosophic, consider this first principle in physiology 

 as settled, any more than any other first principle of 

 it ? The whole is doubt and darkness. 



We are ignorant of how the sap is first imbibed. 

 We are ignorant of what causes it to ascend. We are 

 ignorant of where, or how, it is elaborated. We are 

 ignorant of the office of the leaf. We are ignorant of 

 the office of the pith. We are ignorant of what causes 

 the stem to grow vertically upward. We are ignorant 

 of what causes the branch to grow horizontally, or at 

 any angle with the horizon, upward or downward. We 

 are ignorant of what causes the tap-root to grow ver- 

 tically downward. And we are ignorant of what 

 causes the branch-root to grow horizontally, or at any 

 angle with the .horizon, upward or downward ; or of 



