ch. xvil] INSECTIVOROUS PLANTS. 341 



about Drosera than the origin of all the species in the world. 

 But I will not publish on Drosera till next year, for I am 

 frightened and astounded at my results. I declare it is a 

 certain fact that one organ is so sensitive to touch, that a 

 weight seventy-eight times less than that, viz., t -qVo" f a 

 grain, which will move the best chemical balance, suffices 

 to cause a conspicuous movement. Is it not curious that a 

 plant should be far more sensitive to the touch than any 

 nerve in the human body? Yet I am perfectly sure that 

 this is true. When I am on my hobby-horse, I never can 

 resist telling my friends how well my hobby goes, so you 

 must forgive the rider." 



The work was continued, as a holiday task, at Bourne- 

 mouth, where he stayed during the autumn of 1862. 



A long break now ensued in his work on insectivorous 

 plants, and it was not till 1872 that the subject seriously 

 occupied him again. A passage in a letter to Dr. Asa Gray, 

 written in 1863 or 186-1, shows, however, that the question 

 was not altogether absent from his mind in the interim : 



" Depend on it you are unjust on the merits of my be- 

 loved Drosera ; it is a wonderful plant, or rather a most 

 sagacious animal. I will stick up for Drosera to the day of 

 my death. Heaven knows whether I shall ever publish my 

 pile of experiments on it." 



He notes in his diary that the last proof of the Expres- 

 sion of the Emotions was finished on August 22, 1872, and 

 that he began to work on Drosera on the following day. 



C. D. to Asa Gray. [Sevenoaks], October 22 [1872]. 



... I have worked pretty hard for four or five weeks on 

 Drosera, and then broke down ; so that we took a house near 

 Sevenoaks for three weeks (where I now am) to get com- 

 plete rest. I have very little power of working now, and 

 must put off the rest of the work on Drosera till next spring, 

 as my plants are dying. It is an endless subject, and I must 

 cut it short, and for this reason shall not do much on Di- 

 onaea. The point which has interested me most is tracing 

 the nerves ! which follow the vascular bundles. By a prick 

 with a sharp lancet at a certain point, I can paralyse one- 

 half the leaf, so that a stimulus to the other half causes no 

 movement. It is just like dividing the spinal marrow of a 

 frog : no stimulus can be sent from the brain or anterior 

 part of the spine to the hind legs : but if these latter are 



