excitability and movement of the Leaves of Oxalis. 389 



"After a little while" he observes/' they perceived that one of 

 these plants had changed the position of its leaves, and they at 

 once suspected that it was an irritable plant which I had never 

 mentioned in my lectures. I was in the botanic garden, which 

 is contiguous to the public garden, at the time ; they came and 

 told me of this fact, which was not less new to me than to them. 

 I went with them to the spot, and found that the plant was 

 the Oxalis stricta. This is not mentioned in the list of spe- 

 cies designated by authors as sensitive. I immediately repeated 

 the experiment upon other individuals and obtained the same 

 effect ; but it must be teased a long while, as its movements are 

 much slower than those of the Mimosa pigra. I suspect that 

 if plants were observed with the requisite care, the phenome- 

 non of irritability would not be so rare as is supposed. The 

 irritability of the Oxalis sensiliva is already known. T have 

 made experiments upon all those cultivated in our botanic 

 garden, but I did not succeed in causing the position of the 

 leaves to change. I believe that heat is the principal agent 

 in this phamomenon, because even the Hedysarum gyrans 

 slackens in its movements in autumn and during winter in 

 hothouses. I should think that all the species of Oxalis are 

 susceptible of contraction when irritated ; but as most of them 

 are natives of the Cape of Good Hope, it is possible that they 

 show no effects from concussion in our climate, whose greatest 

 heat never equals that of xifrica. In the environs of Modena 

 we have neither the Oxalis acetosella nor Oxalis corniculata, 

 I have not therefore been able to make experiments upon 

 them." 



M. Morren in addition gives an account of some new ob- 

 servations which this communication had led him to make, 

 and which proved to be in every respect confirmatory of the 

 views of M. De Brignoli. 



" The Oxalis sensitive/, mentioned here by M. De Brignoli, 

 and originally from China, was indeed named by M. DeCan- 

 dolle from this fact Biophytum (Biophytum sensitivum) ; that 

 is to say, plant alive ; its leaves are pinnate like those of Sen- 

 sitive plants. The East Indian Averrhoa bilimbi is another 

 of the Oxalidece in which the leaves are likewise excitable and 

 mobile. The Averrhoa carambola has its petioles mobile, as 



