1 868 1881] BLOOM 409 



that L. flavum never seeds in any garden that I have seen, Letter 735 

 because one form alone is cultivated by slips. 1 



The following five letters refer to Darwin's work on "bloom "-a 

 subject on which he did not live to complete his researches :- 



One of his earliest letters on this subject was addressed in August, 

 1873, to Sir Joseph Hooker : 3 



" I want a little information from you, and if you do not yourself know, 

 please to enquire of some of the wise men of Kew. 



"Why are the leaves and fruit of so many plants protected by a 

 thin layer of waxy matter (like the common cabbage), or with fine hair, 

 so that when such leaves or fruit are immersed in water they appear as 

 if encased in thin glass ? It is really a pretty sight to put a pod of the 

 common pea. or a raspberry, into water. I find several leaves are thus 

 protected on the under surface and not on the upper. 



"How can water injure the leaves, if indeed this is at all the case?" 



On this latter point Darwin wrote to the late Lord Farrer : 



" I am now become mad about drops of water injuring leaves. Please 

 ask Mr. Payne 3 whether he believes, from his own experience, that drops 

 of water injure leaves or fruit in his conservatories. It is said that the 

 drops act as burning-glasses ; if this is true, they would not be at all 

 injurious on cloudy days. As he is so acute a man, I should very much 

 like to hear his opinion. I remember when I grew hothouse orchids 

 I was cautioned not to wet their leaves ; but I never then thought on 

 the subject." 



The next letter, though of later date than some which follow it, is 

 printed here because it briefly sums his results and serves as guide to the 

 letters dealing with the subject. 



To W. Thiselton-Dyer. 4 Letter 736 



Down, Sept. 5th [1877]. 



One word to thank you. I declare, had it not been for 

 your kindness, we should have broken down. As it is we 

 have made out clearly that with some plants (chiefly succu- 

 lent) the bloom checks evaporation with some certainly 

 prevents attacks of insects ; with some sea-shore plants pre- 

 vents injury from salt water, and, I believe, with a few prevents 

 injury from pure water resting on the leaves. This latter 



1 Id est, because, the plant being grown from slips, one form alone 

 usually occurs in any one garden. It is also arguable that it is grown by 

 slips because only one form is common, and therefore seedlings cannot 

 be raised. 



2 Published in Life and Letters, III., p. 339. 



3 Lord Farrer's gardener. 



4 Published in Life and Letters, III., p. 341. 



