Chap, xi Sensitivity and Stimulation 481 



More specialized examples of the power of appreciating 

 contact stimulation are afforded by the so-called insecti- 

 vorous plants, of which but little was known up to i860, 

 but which attracted much attention after that date. They 

 were shown to possess a very specialized apparatus for 

 nutrition, associated with very delicate sensitiveness in 

 more than one direction. Many writers gave careful 

 attention to their biological peculiarities, of whom 

 Nitschke and C. Darwin added most to our knowledge. 

 The work of Nitschke, which was confined to Drosera, 

 was published in i860, and was the first to appear after 

 the memoir by Roth, which was published in 1782. Nitschke 

 gave an account of the movements of the tentacles and 

 described the method of their propagation, which was a very 

 satisfactory piece of work for the time. The subject then 

 fell into neglect and was only brought to the front again 

 by the more elaborate researches of Darwin, published in 

 1875. Darwin did not confine himself to Drosera, but in- 

 vestigated all the then known insectivorous plants, and 

 made clear the bearing of their behaviour on their nutritive 

 processes, and the close correspondence of the latter with 

 gastric and intestinal digestion in mammalian animals, while 

 he showed that not only movement but secretion and 

 chemical change follow stimulation. He demonstrated 

 further their possession of chemotropic as well as tactical 

 perception. 



In the case of Drosera, to which a large part of his 

 memoir was devoted, Darwin gave a full description of the 

 nature of the movement of the tentacles ; the relation of 

 this movement to the area of stimulation in any given case ; 

 the distribution of the sensory areas ; and the conduction 

 of the stimulus from tentacle to tentacle ; pointing out the 

 co-ordination of all, to the end that the digestion and 

 absorption of nitrogenous food material may be secured. 

 He showed that the result of contact stimulation alone 



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