18 A DISCOURSE 



BOOK I. more of these particulars at this time, because the rest are sprinkled over 

 this whole Work in their due places ; wherefore we hasten to the follow- 

 ing title, namely, the choice and ordering of the seeds. 



3. Choose your seed of that which is perfectly mature, ponderous, and 

 sound ; commonly that which is easily shaken from the boughs, or ga- 

 thered about November, immediately upon its spontaneous fall, or taken 

 from the tops and summities of the fairest and soundest trees, is best, 

 and does, for the most part, direct to the proper season of interring, &c. 

 according to institution. 



mental proofs of a circumstance so full of harmony. In January, 1769, being engaged in 

 an investigation of the nature of the Food of vegetables, with a view to establish a theory 

 of Agriculture, I saw that there must be some secret property in the air, which restored 

 ■worn-out lands to their former fertility ; and as I could not persuade myself that it arose 

 from the universal acid, so much talked of, I was led, by a chain of reasoning and some 

 few experiments, to conclude that it must proceed from putrid exhalations, first generated 

 upon the surface of the earth, then raised into the atmosphere, and afterwards brought 

 down by rain : In this manner I supposed that the influence of Heaven, as Mr. Evelyn 

 well expresses it, was obtained. Having fully satisfied myself that worn-out lands were 

 thus restored, I went a step further, and concluded, as I thought with certainty, that all 

 plants, by their leaves as well as by their roots, imbibed these putrid vapours for their 

 food. And here I beg leave to remark, that I do not mean to say that plants have no 

 other nutriment, as it may be proved to a demonstration that many things give them food 

 without having undergone the putrid ferment. March 8, 1769, (two years before Dr. Priestley 

 began any experiments in vegetation,) I read a memoir upon this curious subject before 

 the York Agriculture Society, being the day of their institution ; and in June following I 

 published it in a small duodecimo volume of 66 pages, under the title of Georgical Essays. 

 The favourable reception that this work met with, induced me to republish it in 1770, with 

 considerable additions. The words I refer to are these: " During the summer months the 

 " atmosphere is full of puti-id exhalations arising from the steam of dunghills, the perspi- 

 " ration of animals and smoke. Every shower brings down these oleaginous * particles 

 * The word oiea- « for the nourishment of plants." Geors. Essays, p. 10. " It is pleasing to observe how the 



ginous is chiefly ^ ^ 



applied to smoke, " dissolution of One body is necessary for the life and mcrease of another. All nature is 

 anti corresponds „ |^ motion. In cousequeuce of the putrid fermentation that is every where carried on, 



with the theory of ^ o u 



the food ot plants, "a quantity of vegetable nutriment ascends into the atmosphere. Summer showers 

 described in « rgtum much of it again ; but part falls into the sea and is lost : To this we may add the 

 " animal and vegetable substances consumed on board of ships, all of which are buried in 

 " the ocean. The industry of man restores them to the earth ; and we may presume that 

 " the fish taken from the sea leave a balance in favour of mankind : Thus Provi- 



the essays here 

 quoted 



