EXPERIMENTS ON THE ROOTS OF PLANTS. 515 



which I had formerly the honour of communicating to the Society, 

 have shown that, in fact, vegetables may suffer from the absorption of 

 the poisons which they themselves furnish. The continual elongation 

 of the roots renders the effect hurtful not to the same generation of 

 plants ; it is the following of the same species which suffers from it, 

 while it is possible to imagine that, on the contrary, these same excre- 

 ments will furnish wholesome and abundant nourishment to another 

 order of vegetables. The examples drawn from vegetables here offer 

 themselves again with the force of analogy which is very remarkable. 

 It was still, perhaps, necessary to this very ingenious theory, which 

 accounted so reasonably for most of the facts obtained, to be more 

 clearly confirmed by the results of direct experiments; and by the 

 invitation of M. De Candolle I endeavoured to obtain them. The thing 

 was, however, not very easy, and my first attempts were unavailing. 

 I first strove to obtain the supposed exudation directly from plants 

 plucked up by the roots, but, with the exception of some very doubtful 

 cases, it was impossible ever to obtain any sufficient quantity, and the 

 rapidity with which the plants perished in this state destroyed all 

 chance of succeeding by this means. I afterwards attempted to sow 

 the seeds in substances purely mineral, such as pure siliceous sand, 

 pounded glass, &c. Also on clean sponges, white linen, &c. ; but 

 although they germinated well, the existence of the plants was always 

 short and precarious, and when I endeavoured to collect their exudation 

 by the use of earths, I found that the decomposition of the refuse from 

 the seeds gave the same character to the whole of them, and that a 

 sort of vegeto-animal substance was always obtained, of which it was 

 impossible to mistake the source, and which entirely concealed the 

 results of the real exudation, if any were present in plants so imper- 

 fectly developed. As a last resource, with the use of rain water, the 

 purity of which I had ascertained by the usual reactives, and which 

 left no residue after evaporation, I endeavoured to preserve plants that 

 were entirely developed. Their roots being taken from the ground 

 with the greatest care, I washed them minutely in rain water to 

 remove all the mould, and when they were entirely cleansed from all 

 impurity, they were dried and placed in phials with a certain quantity 

 of water. I soon observed that they flourished in it, developing their 

 leaves, blossoming, and, after some time, giving by the evaporation of 

 water in which their roots were plunged, and by the reactives, evident 

 marks of exudation by the latter. Much time is required for studying 

 a great number of families, and at present I am able to present to the 



