207 



borne on the wings of the winds, they fly acrose the ce- 

 lestial plains, which they adorn with their rich colours, 

 and coniiuually variegated forms. Fixed at length on 

 the mountain tops, they pour upon them abundant rains, 

 which being collected in the vast reservoirs, embosomed 

 within them, furnish, by a happy circulation, a supply 

 to fountains, rivers, lakes and seas. Like veins and ar- 

 teries, the rivers flow meandering, and branching on 

 the surface of the earth, they run through immense 

 dffmitries; water, fertilize, and unite them by a recipro- 

 cal commerce, and majestically rolling their waves to- 

 ward the sea, plunge themselves into it, in order to be 

 again exhaled in vapours, and re-enter afresh into the 

 channels of this magnificent circulation. 



22. Does the sap circulate in plants as the blood cir- 

 culates in animals ? Is this new mark of analogy between 

 these two classes of organized bodies as real as it has 

 appeared to be? Small bladders full of air which have 

 been thought to be discovered within the leaves, 

 have convinced us that they were the lungs of the 

 plant. 



But there have not been discovered in plants vessels 

 analogous to veins and arteries. No organ has been 

 seen in them capable of performing the functions of the 

 heart. A tree which is planted a contrary way, with the 

 roots a top and the branches in the ground, lives, grows, 

 bears fruit ; from its roots, branches shoot forth ; from 

 its branches, roots. The same is observed with respect 

 to slips and layers. A young branch, or young fruit, 

 after being grafted on a subject foreign to itself, incor- 

 porates with it, and derive' from thence the same de- 

 gree of growth it would have received from the plant 

 whence it was detached. Experiments demonstrate, 

 lhat the motion of the sap depends entirely on the alter- 

 natives of heat and cold, and the vicissitudes of day and 

 night. It is evident that the sap rists in the day from 

 the roots to the leaves, and falls in the night from the 

 leaves to the roots. In a word, the course of the sap 

 nearly resembles that of the liquor contained in the tube 



