4 OF THE FOOD OF PLANTS. Parti. 



or to my pulling them off all at once ? Or is there, any particular 

 ftate of plants, in which tliis total ftfipping of them is not of fo 

 fatal confequence ? 



_ The experiments of Mr. Mariotte, Dr. Woodward, and Dr. Hales, 

 prove that the leaves are the organs of perfpiration in plants, and 

 that the greateil part of the fap goes off that way. The reft is 

 fpent in the increaie of the plant. We likewife know that the leaves 

 imbibe the moiiLiire of rain.iind dew, which greatly promotes the 

 growth of the plant. 



In what manner leaves m.ay be imm.ediate organs of the perfpira- 

 tion of plants, or of the preparation of the fap, would be foreign to 

 our purpjfe to inquire into : but that they are organs highly ufeful, 

 appears from the following experiments. 



If half, or two thirds of the leaves of a young tree in full fap are 

 flript off, the tree lofes its fap in two or three days. The bark, 

 which before feparated eafily from the wood, then adheres clolely to 

 it. Before the leaves were fiript off, the tree might be grafted by a 

 fcutcheon i but the next day, the bud cannot be inferted. The tree 

 is therefore weakened by the lofs of its leaves. 



A willow, a poplar, an elm, that is fuffered to grow without be- 

 ing lopped, will remain an age found in the trunk : on the contrary, 

 when turned to pollards, the trunk foon grows rotten. The repeated 

 lopping of tlie branches is therefore very prejudicial. 



The fine fliort grafs which covers the lawns of England, is the 

 only plant that can bear frequent clofe mowing or eating. This 

 grows the more beautiful for it ; but all others are killed thereby. 



What we have faid il:iews, that leaves, in \^'hatever light they are 

 confidered, are of the greateft advantage to plants : and confequently 

 that fain-foin, lucerne, clover, &c. are greatly hurt when thev are 

 fed too clofe by cattle, efpecially when young. We cannot therefore 

 approve the praftice of farmers, who turn in their flocks to feed on 

 their wheat when it is too rank. This we fliall have occafion to 

 fpeak more fully of hereafter. 



CHAP. III. 



Of the Food of P LA NTS. 



SALT, air, fire, water, and earth, form, perhaps, the food of 

 plants. But without entering into that detail, we may, with 

 Mr. TuU, confider earth reduced to very minute particles, as the chief 



piirt 



