i868 1881] PINGUICULA 401 



stream not acting on Dioncea and Drosera. Water does not Letter 724 

 act on the stamens of Berberis^ but it does on the stigma of 

 Mimulus. It causes the flowers of the bedding-out Mesem- 

 bryanthemum and Drosera to close, but it has not this effect 

 on Gazania and the daisy, so I can make out no rule. 



I hope you are going on with Nepenthes ; and if so, you 

 will perhaps like to hear that I have just found out that 

 Pinguicula can digest albumen, gelatine, etc. If a bit of glass 

 or wood is placed on a leaf, the secretion is not increased ; 

 but if an insect or animal-matter is thus placed, the secretion 

 is greatly increased and becomes feebly acid, which was not 

 the case before. I have been astonished and much disturbed 

 by finding that cabbage seeds excite a copious secretion, and 

 am now endeavouring to discover what this means. 1 Probably 

 in a few days' time I shall have to beg a little information 

 from you, so I will write no more now. 



P.S. I heard from Asa Gray a week ago, and he tells me 

 a beautiful fact : not only does the lid of Sarracenia secrete 

 a sweet fluid, but there is a line or trail of sweet exudation 

 down to the ground so as to tempt insects up. 2 



To W. Thiselton-Dyer. Letter 725 



Down, June 2jrd, 1874. 



I wrote to you about a week ago, thanking you for in- 

 formation on cabbage seeds, asking you the name of Luzula 

 or Carex, and on some other points ; and I hope before very 

 long to receive an answer. You must now, if you can, for- 

 give me for being very troublesome, for I am in that state in 

 which I would sacrifice friend or foe. I have ascertained that 

 bits of certain leaves, for instance spinach, excite much 

 secretion in Pinguicula, and that the glands absorb matter 

 from the leaves. Now this morning I have received a lot 

 of leaves from my future daughter-in-law in North Wales, 

 having a surprising number of captured insects on them, a 

 good many leaves, and two seed-capsules. She informs me 

 that the little leaves had excited secretion ; and my son and 



1 Clearly it had not occurred to Darwin that seeds may supply nitro- 

 genous food as well as insects : see Insectivorous Plants^ p. 390. 



2 A dried specimen of Sarracenia^ stuffed with cotton wool, was 

 sometimes brought from his study by Mr. Darwin, and made the subject 

 of a little lecture to visitors of natural history tastes. 



VOL. II. 26 



