Miscellaneous. 469 



all the cells, the substances necessary for their nutrition. These cells 

 assimilate the elements which they require, and reject those which 

 are useless to them. The rejected elements arc taken uj) hy the 

 laticiferous vessels, or collected into peculiar reservoirs, like the 

 essential oils, &c. These reservoirs, however, do not contain a liquid 

 of greater density for which these essential oils liave an affinity. 

 Here again, therefore, endosmose has no part in the movement of the 

 liquids. 



The tendency to admit purely physical causes to explain physio- 

 logical phsenomena is again observed with regard to the spongiole ; 

 for this extremity of the root has been compared to a sponge, as is 

 indicated by its name. Let us see, therefore, how far this comparison 

 is exact. 



In my memoir on the origin of roots, I have shown that the 

 young tissues, the formation of which causes the elongation of the 

 roots, are protected during their development by a sort of little cap, 

 which, for this reason, I called the ]pileorhiza. It actually envelopes 

 the extremity of the root like a cap. This organ may be easily ob- 

 served, especially upon the roots of aquatic plants, because in these 

 the development is more rapid than in most other plants. This cap 

 adheres to the extremity of the root by the interior of its apex ; it is 

 from this point that it is renewed, whilst its outer part, which is 

 oldest, becomes destroyed. The external cells becoming disaggre- 

 gated, could alone have given the idea of a little sponge. AVith 

 regard to the power of absorption, which, at least in certain plants, 

 is much stronger at the extremity of the root than in other parts of 

 that organ, it evidently cannot be assimilated to the capillary phse- 

 nomena which cause liquids to rise in a sponge. The word spongiole, 

 therefore, gives a false idea of that which really takes place in 

 roots. 



Some botanists who admit the spongiole, have nevertheless recog- 

 nized the existence, on the surface of many roots, of prominent cells 

 to which they attribute a share in absorption. I hold their opinion 

 in this respect ; and I am, moreover, led to believe that, even in the 

 woody roots of trees, the whole of the surface is endowed with the 

 property of absorbing liquids from the soil. In trees with a vigorous 

 vegetation, such as Faulownia, I have sometimes had the opportunity 

 of observing, I thhik in the spring, that the dead part of the bark 

 was impregnated with a considerable quantity of liquids, which would 

 probably be yielded to the living parts of the root. 



The liquids absorbed by the roots, by the agency of that force 

 which we only know by its effects — namely life, are conveyed into 

 the ligneous mass of these organs, and thence into that of the stem. 

 These juices rise into the leaves, and then they descend towards the 

 roots, describing a sort of circle. As they pass through the whole 

 extent of the plant, I think that it would be advisable to call this the 

 great circulation, and to give the name of venous circulation to that 

 which, by the laticiferous vessels, conducts the substances which the 

 cells have not assimilated to the true vessels. There is also an intra- 

 cellular movement which has been observed in many vegetables. 



