494 CLIMBING AND INSECTIVOROUS PLANTS. [1862. 



these experiments, together with the previously made remarks 

 on the functions of the parts, I cannot avoid the conclusion, 

 that Drosera possesses matter at least in some degree analo- 

 gous in constitution and function to nervous matter. Now 

 do tell me what you think, as far as you can judge from my 

 abstract; of course many more experiments would have to be 

 tried ; but in former years I tried on the whole leaf, instead 

 of on separate glands, a number of innocuous* substances, 

 such as sugar, gum, starch, &c,, and they produced no effect. 

 Your opinion will aid me in deciding some future year in 

 going on with this subject. I should not have thought it 

 worth attempting, but I had nothing on earth to do. 



My dear Hooker, Yours very sincerely, 



Ch. Darwin. 



P.S. — We return home on Monday 28th. Thank Heaven ! 



[A long break now ensued in his work on insectivorous 

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

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

 written in 1863 or 1864, 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 beloved 

 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 experi- 

 ments 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.] 



* This line of investigation made him wish for information on the ac- 

 tion of poisons on plants ; as in many other cases he applied to Professor 

 Oliver, and in reference to the result wrote to Hooker : " Pray thank Oli- 

 ver heartily for his heap of references on poisons." 



