vn. ur. DOWNWARD GROWTH OF THE ROOTS. lOl 



disputed. 



nature of the sap, as De la Hire ; others, as Darwin, to 

 the hving powers of the plant, and the stimulus of air 

 upon the leaves, and of moisture upon the roots. The 

 effect is now shown to be connected with mechanical 

 causes ; and there seems no other power in nature to 

 which it can with propriety be referred but gravity, 

 which acts universally, and which must tend to dispose 

 the parts to take a uniform direction.' 



I honour and envy the mind which, like Mr. That the 



*' growth of 



Knight's, could foresee the probability of the marvellous ^^^^o^t is 

 result of this beautiful experiment ; and if it is allow- gJ-aTit^ 

 able at all jurare in verba magistri, where is the master 

 whose word we would take sooner than Sir Humphry's ? 

 But surely our great philosopher is here too easily 

 satisfied, at least if he means (as I understand him) 

 that the direction of the growth of plants in general is 

 caused by gravity. I cannot think, myself, that the 

 direction of any of their growth is caused by it. But, 

 on the contrary, as vegetable growth is in opposition 

 to gravity, so I think it is caused by one of the great 

 antagonist powers to the attraction of gravity, and 

 cohesion, — namely, turgescence, or expansion. 



This beautiful experiment, however, relates only 

 to the vertical growth of plants upward and downward ; 

 and has no reference whatever to the growth of either 

 head or root horizontally, or at any angle with the 

 horizontal hue, either upward or downward. Indeed, 

 if the experiment proves anything, it proves that all 

 vegetable growth must be vertical, either upward or 



