OF FOREST-TREES. 



27 



perpetually does about London and for many miles adjacent, as 1 have CHAP, 

 shown in my treatise entitled Fumifugium. 



In the mean time whether water alone is the cause of the solid and 

 bulky part, and consequently of the augmentation of trees and plants, or 

 wdthout any thing more to do with that element than as it serves to trans- 

 port some other matter, is very ingeniously discussed, and curiously in- 

 quired into by Dr. Woodward, in his History of the Earth, fortified with 

 divers nice experiments too large to be here inserted '. The sum is, that 



^ It is of the utmost consequence to determine what is the Food of Plants. Upon that 

 question Philosophers have widely differed. From a number of experiments, accurately 

 conducted, I am led to believe that all vegetables, from the hyssop upon the wall, to the 

 cedar of Lebanon, receive their principal nourishment from oily particles incorporated with 

 water, by means of an alkaline salt or absorbent earth. Until oil is made miscible, it is 

 unable to enter the radical vessels of vegetables ; and, on that account, Providence has 

 bountifully supplied all natural soils with chalky or other absorbent particles. I say na- 

 tural soils ; for those which have been assisted by art are full of materials for that purpose ; 

 such as lime, marl, soap-ashes, and the volatile alkaline salt of putrid dunghills. It 

 may be asked, whence do natural soils receive their oily particles ? I answer, the air 

 supplies them. During the summer months, the atmosphere is full of exhalations 

 arising from the steam of dunghills, the perspiration of animals, and smoke. Every 

 shower brings down these putrescent and oleaginous particles for the nourishment of 

 plants. Of these particles, some fall into the sea, where they probably serve for the 

 nourishment of fuci, and other submarine plants. They are, however, but seemingly lost, 

 as the fish taken from the sea, and the weeds thrown upon the beach, restore them again 

 under a different form. Thus Providence, with the most consummate wisdom, keeps up 

 the necessary rotation of things. 



Haud igitur penitus pereunt quascumque videntur: 

 Quando aliud ex alio reficit Natura : nee ullam 



Rem gigni patitur, nisi morte adjutam aliena. LucRET. 

 The ingenious Mr. Tull, and others, contend that earth is the food of plants. If so, all 

 soils equally tilled would prove equally prolific. The increased fertility of a well-pulverised 

 soil, induced him to imagine that the plough could so minutely divide the particles of 

 earth, as to fit them for entering into the roots of plants. An open soil, if not too light in 

 its own nature, will always pfoduce plentiful crops. It readily receives the air, rainsj 

 and dews into its bosom, and at the same time gives the roots of plants a free passage in 

 quest of food. This is the true reason why land well tilled is so remarkably fruitful.— 

 Wat6r is thought, by some, to be the food of vegetables, when in reality it is only the 

 vehicle of nourishment. Water is an heterogeneous fluid, and is no where to be found 

 purei It always contains a solution of animal or vegetable substances. These constitute 

 the nourishment of plants, and the element in which they are minutely suspended, acts 

 only as a vehicle, in guiding them through the fine vessels of the vegetable body. The 



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