EXPERIMENTS FOR DARWIN 158 



as the waxy secretion is often more conspicuous on the 

 upper leaf surface. 



The prevalence of indumentum on the under surface 

 points to transposition in some cases ; in others perhaps 

 it is a provision against the attacks of insects, which harbor 

 on under surfaces. 



I can quite fancy water impeding both the actinic and 

 calorific effects of sunlight on the leaf. We find watering 

 most prejudicial in the hot sun. It is a splendid subject 

 for experiments. 



Darwin immediately followed this up. He must hear more 

 ibout the rationale of watering in sunlight when Hooker came 

 )n his promised visit the following week. This elicited the 

 rejoinder : 



I am aghast at the prospect of being cross-questioned on 

 the subject of effect of watering in sunshine, and fear that 

 no amount of ingenious wriggling will save me from the 

 reputation of an ignorant pretender to the post of Director 

 of Kew. (August 21.) 



As regards carnivorous plants, the first reference to Darwin's 

 researches is in a letter of January 7, 1873. 



I have wandered away from Drosera and the question 

 you put. In so far as I can remember it is an accepted 

 dogma that there is no cutaneous absorption in living plants, 

 and that glandular hairs are excretory only. I will however 

 ask Dyer, who is away with a cold — he is translating Sachs, 1 

 and will be up to the latest discoveries. I will also ask 

 Berkeley. 



Your aggregation of the protoplasmic contents of the 

 cell reminds me of the contraction of the chlorophyll contents 

 and (?) inner cell wall of the cells under sunlight in a Sela- 

 ginella (serpens I think). Have you tried Begonia leaves, 

 or shall I look out for some plants with hyaline bladdery 

 epidermal cells for you to operate upon ? Can you correlate 

 the specific action of the Ammonia on the protoplasm of 

 the cells, with that of its effect on the blood of animals 



1 A translation of Sachs's Text- Book of Botany, by A. W. Bennett and 

 W. T. Thiselton Dyer, was published in 1875. 



vol. n l 



