396 BOTANY [Chap. XI 



Letter 717 a very remarkable fact? It seems so to me, in my ignorance. 

 I wish I could remember more distinctly what I formerly read 

 of Du Bois Raymond's results. My poor memory never serves 

 me for more than a vague guide. I really think you ought to 

 try Drosera. In a weak solution of phosphate of ammonia 

 (viz. 1 gr. to 20 oz. of water) it will contract in about five 

 minutes, and even more quickly in pure warm water ; but 

 then water, I suppose, would prevent your trial. I forget, but 

 I think it contracts pretty quickly {i.e. in an hour or two) 

 with a large drop of a rather stronger solution of the 

 phosphate, or with an atom of raw meat on the disc of 

 the leaf. 



Letter 718 To J. D. Hooker. 



Oct. 31st, 1873. 



Now I want to tell you, for my own pleasure, about the 

 movements of Desmodium. 



(1) When the plant goes to sleep, the terminal leaflets 

 hang vertically down, but the petioles move up towards the 

 axis, so that the dependent leaves are all crowded round it. 

 The little leaflets never go to sleep, and this seems to me 

 very odd ; they are at their games of play as late as 1 1 o'clock 

 at night and probably later. 1 



(2) If the plant is shaken or syringed with tepid water, 

 the terminal leaflets move down through about an angle of 

 45°, and the petioles likewise move about n° downwards ; so 

 that they move in an opposite direction to what they do when 

 they go to sleep. Cold water or air produces the same effect 

 as does shaking. The little leaflets are not in the least affected 

 by the plant being shaken or syringed. I have no doubt, 

 from various facts, that the downward movement of the 

 terminal leaflets and petioles from shaking and syringing is 

 to save them from injury from warm rain. 



(3) The axis, the main petiole, and the terminal leaflets 

 are all, when the temperature is high, in constant movement, 

 just like that of climbing plants. This movement seems to 



1 Stahl (Botanische Zeifung, 1897, p. 97) has suggested that the 

 movements of the dwarf leaflets in Desmodium serve to shake the large 

 terminal leaflets, and thus increase transpiration. According to Stahl's 

 view their movement would be more useful at night than by day, because 

 stagnation of the transpiration -current is more likely to occur at night. 



