^26 VEGETABLE ORGANOGRAPHY. 



of tlie cellular envelope, which prevents -the juices from 

 reaching them laterally. Lastly, Senebier has shown it 

 by a direct experiment made upon the nearly simple 

 roots of the Carrot: he plunged one entirely into water, 

 and of another he only put the extremity in ; in both 

 cases he saw that the absorption was perceptibly equal : 

 afterwards he took two others, putting the extremity of 

 one into the water, and plunging in the whole surface 

 of the other, with the exception of its extremity, w^hich 

 was raised in such a manner as to be out of the water ; 

 the first absorbed as usual, but the second did not in 

 the least. It is certain, then, that the absorption of 

 roots only takes place by their extremities ; we may 

 here mention that it is, then, at the extremities of the 

 roots, and not at the base of the trunk, that we ought 

 to apply water, manure, and in general all the substances 

 which we wish plants to absorb. 



In the natural state of things, roots always having a 

 tendency to proceed away from their point of origin, 

 either in a vertical direction or in a horizontal one, 

 constantly meet with new strata of earth, the nourish- 

 ment of which has not been exhausted ; and as to 

 natural watering, as there is generally a certain relation 

 between the size of the cyme of a tree and the length 

 of its natural roots, it is found that the rain, after 

 having fallen upon the cyme, drops naturally at the 

 most convenient distance from the trunk to reach the 

 extremity of the roots. 



The division of the radical fibres has the utility of se- 

 parating the spongioles, in such a manner that each of 

 them placed in a situation distinct from the neighbour- 

 ing ones finds some sap to di'aw up. Those which have 

 few or no ramifications have all their spongioles placed 

 at the same point; whence it results; — 1st, that they 

 ought to exhaust of juices this fixed place in a more 



