the two sides, for they are too rapid to be the effect of so slow a 

 process ; but that they are the result of a vital property residing in 

 the organ, on which the poisons act as they do on the sensitive 

 plant. 



The second section relates to the direction of stems towards the 

 light. After having described the nature of the phenomenon, and 

 stated the explanation of it given by De Candolle, namely, the bend- 

 ing of the stem by an accumulation of carbon and the consequent 

 hardening of the side most acted upon by light, the author endea- 

 vours to ascertain if the light exercises a real attraction for the green 

 parts of plants. He operated on naturally floating plants, such as 

 the duckweed {Lemna minor and Polyrhina), and on different species 

 of other plants placed on cork floats. He placed each of them on 

 water in vases which were partly darkened by screens, and he never 

 saw the plants receiving from the light an impulsion which brought 

 the floats away from the spot where they had been placed. When the 

 plants, fully developed, were kept in the dark part of the vase, there 

 sprouted from the neck of the root a new stem, slender and blanched, 

 that ran all along the water so as to reach the diaphragm, and then 

 gave out leaves and grew erect; but the float was never attracted 

 towards the light, although the new stem which the plant had to 

 produce was often three feet and more in length. In the course of 

 these experiments, he had occasion to notice the tendency of roots 

 when developed in the light in water, to take a spiral shape, and 

 found that the white light appears to favour the production of radi- 

 cular fibrils, while, on the contrary, the blue light opposes it. 



In examining the grounds of Dutrochet's theory on the existence 

 in stems of two systems of cells and fibres decreasing in size from 

 the circumference to the centre, and from the centre to the circum- 

 ference, by which he explains by endosmose the bending of the 

 stem, the author has found that this bending in contrary directions 

 of the two parts of a stem slit longitudinally has nothing to do with 

 light. In cutting the stem in various directions, it always bends 

 outwards by the swelling of the cells and the resistance of the cuti- 

 cle, and does not bend at all if this last is removed or slit across in 

 two or three places. 



To ascertain if the sap could be supposed to travel by endosmose 

 from cell to cell, he placed within one another three endosmose 

 tubes filled with a solution of sugar; the last, or largest, plunging 

 in water. This was the only one in which any endosmose was visi- 

 ble, the difference in density from the others being insuflicient to 

 produce it. It is probable that it would be the same for the cells 

 of plants ; and some facts have induced him to think that the liquids 

 penetrate chiefly through the intercellular spaces of the vegetable 

 tissue. He has assured himself by experiments that neither heat 

 nor light have any influence in increasing the quantity or the rapi- 

 dity of endosmose, and he is, consequently, little inclined to admit 

 this phenomenon as exercising the influence sometimes attributed to 

 it in vegetation, and especially in the inclination of stems towards 

 the light. 



