113 



either Change insensibly in the ground, or actually con* 

 tain earthy parts ; or the water which moistens them is 

 itself charged with these particles, which the organs ex- 

 tract, prepare, and assimilate. 



After having been admitted into the body of the root 

 by the extremity of the fibres, the nutritious juice rises 

 into the ligneous fibres, from the trunk or stalk, and 

 passes into the utricle^ that adhere to them : it is there 

 prepared and digested. It afterwards enters into the 

 proper vessels, under the form of a coloured fluid, more 

 or less thick, which we may conjecture to be with re- 

 spect to the plant, what the chyle or blood is to the 

 animal. Being filtered by finer, or more winding pipes, 

 it is at last conveyed to all the parts, whereto it unites 

 itself, and increases their bulk. 



The extreme fineness of the canals for the sap, which 

 renders them, in some measure, capillary pipes; the 

 action of the air on the elastic sheaths of the air-vents, 

 and the impression of these last on the ligneous fibres they 

 contain, or by which they are comprised ; the heat that 

 rarefies the sap ; and, above all, that which, by acting on 

 the surface of the leaves, draws thither the superfluous 

 nutritious juice, and occasions the evaporation of it, 

 seem to be the principal causes of the ascent of this 

 fluid in plants. The quantity of nutriment which a plant 

 derives from the earth, is in proportion to the number 

 and size of its leaves ; the smaller or fewer in number 

 the leaves are, the less it draws. The nutrition of ve- 

 getables is likewise effected immediately by their leaves. 

 Thev '<o not only serve for raising the sap, preparing it, 

 and discharging its superfluity ; they are, moreover, -a 

 kind of roots that pump from the air the juices they 

 transmit to the neighbouring parts. 



The dew, which rises from the ground, is the princi- 

 pal foundation of this aerial nourishment. The leaves 

 present it to their inferior surface, which is always fur- 

 spshed with an infinite number of small pipes that are 

 always ready to observe it; and that the leaves may re- 

 ceive no prejudice in the exercise of this function, they 

 are disposed with such art on the stalk and branches, 



