324 CLIMBING AND [lS/3- 



4. I must tell you my final result, of which I am sure,, 

 [as to] the sensitiveness of Drosera. I made a solution of 

 one part of phosphate of ammonia by weight to 2 1 8, 75 

 of water ; of this solution I gave so much that a leaf 

 got -g-oW f a g ra -i n f trie- phosphate. I then counted the 

 glands, and each could have got only 733 J^y of a grain ; 

 this being absorbed by the glands, sufficed to cause the 

 tentacles bearing these glands to bend through an angle of 

 1 80. Such sensitiveness requires hot weather, and carefully 

 selected young yet mature leaves. It strikes me as a 

 wonderful fact. I must add that I took every precaution, by 

 trying numerous leaves at the same time in the solution and 

 in the same water which was used for making the solution. 



5. If you can persuade your friend to try the effects of 

 carbonate of ammonia on the aggregation of the white blood 

 corpuscles, I should very much like to hear the result. 



I hope this letter will not have wearied you. 



Believe me, yours very sincerely, 



CHARLES DARWIN. 



C. Darwin to W. Thiselton Dyer. 



Down, 24 [December 1873 ?] 



MY DEAR MR. DYER, I fear that you will think me a 

 great bore, but I cannot resist telling you that I have just 

 found out that the leaves of Pinguicula possess a beautifully 

 adapted power of movement. Last night I put on a row of 

 little flies near one edge of two youngish leaves ; and after 14. 

 hours these edges are beautifully folded over so as to clasp 

 the flies, thus bringing the glands into contact with the upper 

 surfaces of the flies, and they are now secreting copiously 

 above and below the flies and no doubt absorbing. The acid 

 secretion has run down the channelled edge and has collected 

 in the spoon-shaped extremity, where no doubt the glands 

 are absorbing the delicious soup. The leaf on one side looks 





