400 BOTANY [CHAP. XI 



Letter 722 I am writing this away from home, and I have come away 

 to get some rest, having been a good deal overworked. I shall 

 read your book with great interest when published, but will 

 not trouble you to send the MS., as I really have no spare 

 strength or time. I believe that your book, judging by the 

 chapter sent, will be extremely valuable. 



Letter 723 To J. D. Hooker. 



The following letter refers to Darwin's prediction as to the manner in 

 which Hedychium (Zinzibe racea?.) is fertilised. Sir J. D. Hooker seems 

 to have made inquiries in India in consequence of which Darwin received 

 specimens of the moth which there visits the flower, unfortunately so 

 much broken as to be useless (see Life and Letters, III., p. 284). 



Down, March 25th [1874]. 



I am glad to hear about the Hedychium, and how soon 

 you have got an answer ! I hope that the wings of the 

 Sphinx will hereafter prove to be bedaubed with pollen, for 

 the case will then prove a fine bit of prophecy from the 

 structure of a flower to special and new means of fertilisation. 



By the way, I suppose you have noticed what a grand 

 appearance the plant makes when the green capsules open, 

 and display the orange and crimson seeds and interior, so as 

 to attract birds, like the pale buff flowers to attract dusk- 

 flying lepicloptera. I presume you do not want seeds of 

 this plant, as I have plenty from artificial fertilisation. 



In Natiire, June 22nd, 1876, p. 173, Hermann Muller communicated 

 F. Miiller's observation on the fertilisation of a bright-red-flowered 

 species of Hedychium, which is visited by Callidryas^ chiefly the males 

 of C. Pkilea, The pollen is carried by the tips of the butterfly's wing, 

 to which it is temporarily fixed by the slimy layer produced by the 

 degeneration of the anther-wall. 



Letter 724 T W. Thiselton-Dyer. 



Down, June 4th [1874]. 



1 am greatly obliged to you about the Opuntia, and shall 

 be glad if you can remember Catalpa. I wish some facts on 

 the action of water, 1 because I have been so surprised at a 



1 See Pfeffer, Untersuchungen Bot. Inst. zu Tubingen, Bd. I., 1885, 

 p. 518. Pfeffer shows that in some cases Drosera, for instance water 

 produces movement only when it contains fine particles in suspension. 

 According to Pfeffer the stamens of Berberis, and the stigma of Mimnlus, 

 are both stimulated by gelatine, the action of which is, generally speaking, 

 equivalent to that of water, 



