i88i.] 'POWER OF MOVEMENT IN PLANTS.' 509 



often used by scientific men towards each other does no good, 

 and only degrades science. 



I have been profoundly interested by your book, and some 

 of your experiments are so beautiful, that I actually felt 

 pleasure while being vivisected. It would take up too much 

 space to discuss all the important topics in your book. I fear 

 that you have quite upset the interpretation which I have 

 given of the effects of cutting off the tips of horizontally 

 extended roots, and of those laterally exposed to moisture ; 

 but I cannot persuade myself that the horizontal position of 

 lateral branches and roots is dae simply to their lessened 

 power of growth. Nor when I think of my experiments with 

 the cotyledons of Fhalaris, can I give up the belief of the 

 transmission of some stimulus due to light from the upper 

 to the lower part. At p. 60 you have misunderstood my 

 meaning, when you say that I believe that the effects from 

 light are transmitted to a part which is not itself heliotropic. 

 I never considered whether or not the short part beneath the 

 ground vv^as heliotropic ; but I believe that with' young seed- 

 lings the part which bends Jiear^ but above the ground is 

 heliotropic, and I believe so from this part bending only 

 moderately when the light is oblique, and bending rectan- 

 gularly when the light is horizontal. Nevertheless the bend- 

 ing of this lower part, as I conclude from my experiments 

 with opaque caps, is influenced by the action of light on the 

 upper part. My opinion, however, on the above and many 

 other points, signifies very little, for I have no doubt that 

 your book will convince most botanists that I am wrong in all 

 the points on which we differ. 



Independently of the question of transmission, my mind is 

 so full of facts leading me to believe that light, gravity, &c., 

 act not in a direct manner on growth, but as stimuli, that I 

 am quite unable to modify my judgment on this head. I 

 could not understand the passage at p. 78, until I consulted 

 my son George, who is a mathematician. He supposes that 

 your objection is founded on the diffused light from the lamp 

 illuminating both sides of the object, and not being reduced, 



