398 ON THE SUPPOSED BOTANICAL PROOFS OF THE 



for, as has been already shown, it is founded on a confusion 

 between the true cause of a phenomenon and one of the conditions 

 which are necessary for its production. We might as well con- 

 sider the phenomena of geotropism^ Jtydrotropittm, and heliot-ropiftm 

 which have been established, and investigated in such a brilliant 

 way by modern vegetable physiologists as the direct results 

 of the attraction of the earth, of water, and of light ; and it is 

 not improbable that some botanists are even inclined to make this 

 assumption. And yet it is perfectly easy to show that this cannot 

 be the case. By geotropism we mean the power possessed by the 

 parts of a plant of growing along lines which make certain 

 angles with the direction of the earth's attraction. For example, 

 the chief root grows parallel with the earth's attraction, viz. towards 

 the centre of the earth, and it is described as positively geotropic : 

 conversely the main shoot grows along the same line but in an 

 opposite direction, and it is negatively geotropic. But geotropism 

 is not a primitive attribute of the plant, and it is even now absent 

 from those plants which, like many Algae, have no definite position. 

 Geotropism cannot have arisen before plants first became fixed in 

 the earth. If any one were to assume that the direct influence of 

 gravity, continuous through countless generations, had at length 

 conferred upon the root the power of growing in a geotropic direc- 

 tion, how would it be possible to explain the fact that the shoot 

 which has been under precisely the same influence has acquired the 

 power of growing in an exactly opposite direction ? The character- 

 istic differences between root and shoot cannot have appeared until 

 the plant became fixed in the ground, and how can we imagine that 

 the same influence of gravity has since that time directly produced 

 the two antagonistic results of positive and negative geotropism, 

 in two structures, which were originally and essentially similar ? It 

 should also be remembered that it is only the main root which 

 exhibits true positive geotropism. The lateral roots form angles 

 with the main root, and do not therefore grow towards the earth's 

 centre ; and the same is true of the lateral shoots which grow 

 obliquely, and not perpendicularly upwards, like the main shoot. 

 Moreover the angles which the lateral roots make with the main 

 root, and the lateral shoots with the main shoot, are quite different 

 in different species. How is it possible that all these different 

 modes of reaction witnessed in the different parts of plants can be 



