390 Prof. De Brignoli and Prof. Morren on tin' 



- 



Bruce has shown*. These approximations prove that the 

 movement of the leaves of the true Oxalides may in fact ex- 

 tend to a multitude of species, since this genus is one of the 

 most numerous f. 



During the great heats of the month of June, when the 

 thermometer was at + .35° (R.) in the sun, the excitability and 

 movement of the leaves were very evident in our three indi- 

 genous species of Oxalis : Oxalis acetosella, Oxalis stricta, and 

 Oralis corniculata. When the sun darts his rays in the mid- 

 dle of the day directly on the leaves of these plants, their three 

 obcordate leaflets are level, horizontal, and so placed that the 

 margins which are directed towards the point of the heart, or 

 towards the very short partial petiole, nearly touch one an- 

 other ; so that then there is, so to say, no space between the 

 leaflets. This is the position of repose. Now if we strike the 

 common petiole with light but repeated blows, or if we agi- 

 tate by the same means the entire plant, we see, after the space 

 of a minute, — less if it be very hot, more if it be cool, — three 

 phaenomena take place. 



1. The leaflets fold themselves up along their midrib just 

 like the moveable limb of the Dionea muscipula, in such a 

 manner that their two halves approach each other by their 

 upper surface ; the movement therefore in this case is from 

 below upwards, and it is a folding together. 



2. Each lobe of the leaflet bends inwards, so that outwardly 

 and on its lower surface it presents a convexity more or less 

 decided. This is a movement of incurvation. 



3. Each partial petiole, although very short, bends itself 

 from above downwards, so as to cause the leaflets to hang 

 downwards, which then nearly touch each other by their 



* Phil. Trans, vol. lxxv. p. 356. An Account of the sensitive qualities of 

 the tree Averrhoa carambola. 



t M. Virey, in a paper entitled, " Quelques considerations nouvelles sur 

 l'acidite dans les plantes irritables," (Journal de Pharmacie, Paris, 1839, 

 No. V. 25e annee, Mai, p. 289,) has fallen into three mistakes in what he says 

 of the irritability of the Biophytum and of the Averrhoce. In the first place 

 he confounds the two genera in making Biophyta of the Averrhoa bilimbi 

 and Averrhoa carambola, which is not the case. In the next place, the Ox- 

 alis sensitiva being the same plant as the Biophytum sensitivum of DeCan- 

 dolle, it is by no means the stamina which are excitable, but the leaves, as 

 all authors say. Lastly, M. Virey has taken the Oxalis sensitiva for a plant 

 distinct from the Biophytum. 



