410 BOTANY [CHAP. Xi 



Letter 736 is as yet the most doubtful and the most interesting point 

 in relation to the movements of plants. 



Modern research, especially that of Stahl on transpiration (Bof. 

 Zcitung, 1897, p. 71) has shown that the question is more complex than 

 it appeared in 1877. Stahl's point of view is that moisture remaining on a 

 leaf checks the transpiration-current ; and by thus diminishing the flow 

 of mineral nutriment interferes with the process of assimilation. Stahl's 

 idea is doubtless applicable to the whole problem of bloom on leaves. 

 For other references to bloom see Letters 685, 689 (p. 368), 693. 



To J. D. Hooker. 



Letter 737 Down, Aug. i 9 th, 1873. 



The next time you walk round the garden ask Mr. Smith, 1 

 or any of your best men, what they think about injury from 

 watering during sunshine. One of your men viz., Mr. Payne, 

 at Abinger, who seems very acute declares that you may 

 water safely any plant out of doors in sunshine, and that you 

 may do the same for plants under glass if the sashes are 

 opened. This seems to me very odd, but he seems positive 

 on the point, and acts on it in raising splendid grapes. 

 Another good gardener maintains that it is only cold water 

 dripping often on the same point of a leaf that ever injures 

 it. I am utterly perplexed, but interested on the point. 

 Give me what you learn when you come to Down. 



I should like to hear what plants are believed to be most 

 injured by being watered in sunshine, so that I might get such. 



I expect that I shall be utterly beaten, as on so many 

 other points ; but I intend to make a few experiments and 

 observations. I have already convinced myself that drops 

 of water do not act as burning lenses. 



To J. D. Hooker. 



Letter 738 J 



Dec. 20th [1873]. 



I find that it is no use going on with my experiments 

 on the evil effects of water on bloom-divested leaves. Either 

 I erred in the early autumn or summer in some incompre- 

 hensible manner, or, as I suspect to be the case, water is only 

 injurious to leaves when there is a good supply of actinic 

 rays. I cannot believe that I am all in the wrong about the 

 movements of the leaves to shoot off water. 



1 Probably John Smith (1798-1888), for some years Curator, Royal 

 Gardens, Kew. 



