A I R 



A I R 



reduced, the advantage of frequent digging, or 

 turning over the earth, in the practice of garden- 

 ing, is rendered sufficiently evident. 



Besides, as the heat of the air is given out in 

 the union of oxygen with carbon, as is fully de- 

 monstrated by the heat that takes place in hot- 

 beds ; it would seem to show, that in the culture 

 of roots or plants, the seeds and sets should be 

 sown and put into the ground as soon as possible 

 after the beds have been dug over, while the 

 above processes are going on, and the heat is 

 evolving, as by this means their vegetation 

 and growth may be the most effectually pro- 

 moted. 



Air was considered by the learned Dr. IJales 

 to be a fine elastic fluid, with particles of very 

 different natures floating in it, whereby it was ad- 

 mirably fitted, by the great Author of nature, 

 to be the breath or life of vegetables as well 

 as animals, without which they could no more 

 live and thrive than animals ; and as a proof of 

 the great quantities of it in vegetables, he refers 

 to the third chapter of his excellent Treatise on 

 Vegetable Statics, where he remarks, in the ex- 

 periments on vines, that a great quantity of air 

 was visible, which was continually ascending 

 through the sap into the tubes ; which manifestly 

 shows what plenty of it is taken in by vegetables, 

 and is perspired off with the sap through the 

 leaves. He likewise details several experiments 

 made on branches of apple, apricot, birch, and 

 other trees, to prove the same thing. 



And Dr. Grew remarks, that the pores arc so 

 large in the trunks of some plants, as in the 

 bettci sort of thick walking-canes, that thev are 

 visible to a good eye without a glass : but with 

 a glass the cane seems as if stuck at top full 

 of holes with great pins, so large as verv well to 

 resemble the pores of the skin in the ends of the 

 fingers and ball of the hand. In the leaves of 

 pines he likewise observes, that by means of 

 a glass they make a very elegant show, standing 

 almost exactly in rank and file through the length 

 of the leaves ; whence he thinks it may be pro- 

 bable that the air enters plants, not only with the 

 principal food or nourishment by the root, but 

 also through the surface of their trunks and 

 leaves, especially at night, when they are changed 

 from a perspirina; to a strongly imbibing state. 



It is observed by the former of these writers, 

 however, that in all the experiments he tried for 

 this purpose, he found that the air entered very 

 slowly at the bark of young shoots and branches, 

 but much more freely through old bark ; and 

 that in different kinds of trees it had different 

 degrees, or more or less freedom of entrance : 

 and likewise that there is a portion of air both in 

 an elastic and unelastie state, mixed with earthy 



matter, as he found by several experiments 

 which are detailed in his work. 



Air. Bovle also, in making experiments on 

 air, among other discoveries, found that a good 

 quantity of it was producible from vegetables, 

 by putting grapes, plums, gooseberries, peas, and 

 several other sorts of fruit and grain, into ex- 

 hausted and unexhausted receivers, where they 

 continued for several days, emitting great quan- 

 tities of air. These led Dr. Hales to further re- 

 searches on the subject, in order to discover what 

 proportion of air he could obtain from the vege- 

 tables in which it was lodged and incorporated; and 

 he concluded that it was abundant in vegetable 

 substances, and bore a considerable part in them. 



Some kinds of earth, as well as substances of 

 the manure kind, are found to contain much 

 larger proportions of airs, and to yield or part 

 with them with much greater ease and facility 

 than others : a circumstance which has much in- 

 fluence in the practice of gardening, and the 

 growth of different sorts of vegetables. ' 



Numerous experiments that have been more 

 recently made, have, however, in consequence 

 of the knowledge that has been acquired of the 

 constituent principles of the air, from the inge- 

 nious inquiries of Black, Cavendish, Priestley, and 

 others in our own country, and the exertions of 

 Lavoisier and other chemical philosophers on the 

 continent, brought us more fullv acquainted 

 with the causes of the numerous beneficial ef- 

 fects that are daily produced on vegetation by 

 the agency of the atmospheric air. 



It has been ascertained, that both of the prin- 

 ciples which constitute atmospheric air are highly 

 beneficial in the oeconoiny of plants; and "that 

 by their different combinations with other mat- 

 ters they contribute greatlv to vegetation, as has 

 been already seen. 



And it has been shown above, that the vegeta- 

 tive process of grain, seed, and other vegetal les, is 

 greatly promoted by the free and easy acces* of 

 the air; which strongly enforces the necessity- of 

 pulverizing and rendering the soil in a state of 

 considerable linuu-ss before they are introduced 

 into it. Seeds and plants can grow in the mois- 

 ture of the air, and in water, without the inter- 

 vention of earth; but neither of these is suffi- 

 cient for the purpose without the free admission 

 of air. Many plants of the succulent kind retain 

 their vegetative quality a considerable length of 

 time, merely by the agency of the air ; and" some 

 emit roots from the branches that are cut from 

 them, on being exposed to the air, without the 

 assisianee of either earth or water. The Sedum 

 and Sempervivwrri afford examples of this kind. 

 Air is likewise necessary in order to preserve the 

 vegetative faculty of grains and seeds while they 

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