ch. xvil] MOVEMENTS IN PLANTS. 339 



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 con- 

 sulted my son George, who is a mathematician. He sup- 

 poses that your objection is founded on the diffused light 

 from the lamp illuminating both sides of the object, and 

 not being reduced, with increasing distance in the same 

 ratio as the direct light ; but he doubts whether this neces- 

 sary correction will account for the very little difference 

 in the helio tropic curvature of the plants in the successive 

 pots. 



With respect to the sensitiveness of the tips of roots to 

 contact, I cannot admit your view until it is proved that I 

 am in error about bits of card attached by liquid gum caus- 

 ing movement ; whereas no movement was caused if the 

 card remained separated from the tip by a layer of the liquid 

 gum. The fact also of thicker and thinner bits of card at- 

 tached on opposite sides of the same root by shellac, causing 

 movement in one direction, has to be explained. You often 

 speak of the tip having been injured ; but externally there 

 was no sign of injury : and when the tip was plainly injured, 

 the extreme part became curved towards the injured side. 

 I can no more believe that the tip was injured by the bits 

 of card, at least when attached by gum-water, than that the 

 glands of Drosera are injured by a particle of thread or hair 

 placed on it, or that the human tongue is so when it feels 

 any such object. 



About the most important subject in my book, namely, 

 circumnutation, I can only say that I feel utterly bewildered 

 at the difference in our conclusions ; but I could not fully 

 understand some parts which my son Francis will be able to 

 translate to me when he returns home. The greater part 

 of your book is beautifully clear. 



Finally, I wish that I had enough strength and spirit to 

 commence a fresh set of experiments, and publish the 

 results, with a full recantation of my errors when con- 

 vinced of them ; but I am too old for such an undertaking, 

 nor do I suppose that I shall be able to do much, or any 

 more, original work. I imagine that I see one possible 

 source of error in your beautiful experiment of a plant ro- 

 tating and exposed to a lateral light. 



With high respect, and with sincere thanks for the kind 



