A I R 



A I R 



reduced, tlie advantage of frequent digging, nr 

 turnins ovi-r the earth, in the pracliccof gardcn- 

 inii", is rendered sutliciently evident. 



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

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

 monstrated bv tiie heat that takes place in hot- 

 beds ; it w ouid seem to show, th;ct in tlie 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 arc going on, and the heat is 

 evolving, as by this means their vegetation 

 and growth may be the most eflectually pro- 

 moted. 



Air was considered by the learned Dr. Hales 

 to be a line elastic fluid, with particles of very 

 difterent natures floating in it, whereby it was ad- 

 mirably litted, 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 a^ a proof of 

 the crcat quantities of it in vegetables, he refers 

 to the third chapter of his excellent Treatise on 

 Veiretable 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 ofl" with the sap through the 

 leaves. He likew ise details several experiments 

 made on branches of apple, apricot, birch, and 

 other trees, to prove the same thing. 



And Dr. Crew remarks, that the pores are so 

 larse in the truiiks of some plants, as in the 

 betlej sort of thick walking-canes, that they are 

 visible to a coed eye without a glass : but with 

 a elass the cane seems as if stuck at top lull 

 ofliolcs with great pins, so large as very well to 

 resemble the pores of the skin in the ends of the 

 lingers anil Inill of the hand. In the leaves of 

 nines he likewise observes, that bv means of 

 a glass ihcv make a very elegant show, standing 

 almost exactly in rank and file through the length 

 of the leaves ; w hence he thinks it may be pro- 

 liable that the air enters plants, not only with the 

 principal I'ood or nourishment by the root, but 

 also liirouiih the surface of their trunks and 

 leaves, cspeeiallv at nitht, when ihcy arcclianged 

 from a perspirinsr to a strongly imbibing state. 



It is observed Lv the former of these writers, 

 however, that in all the experiments he tried for 

 this purpose, he i'ound that tli- air entered very 

 slowly at the bark <jf young shoots and branches, 

 but nuich more IVeclv through old bark ; and 

 that in difierent kinds of trees it had diiferent 

 desrrees, or more or less freedom of entrance : 

 and likewise that there is a portion of air both in 

 ia clastic and uiiclaatic stalCj mi.\ed w iih earthy 



matter, as he found by several cxperinK-nls 

 which are detailed in his work. 



Mr. Boyle also, in making experiments on 

 air, among other discoveries, found that a good 

 quantity of it was ])roduciblc from vegetables, 

 by puttintr crapes, plums, gooseberries, pea.*, and 

 several other sorts of fruit and grain, into ex- 

 hausted and unexhausted receivers, where they 

 continued for several days, cniitiing great quim- 

 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 tlieni 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 

 w ith the causes of the numerous beueticial ef- 

 fects that are daily produced on vcgelatian by 

 the agency of the atmospheric air. 



It has been ascertained, ihat both of the prin- 

 ciples w hich constitute atmospheric air are highly 

 beneficial in the ceconomy of plants ; and tiiat 

 by their different combinations w ith other mat- 

 ters they contribute greatly to vegetation, as ha* 

 been already seen. 



And it has been shown above, that tlu- vegeta- 

 tive process of grain, seed, and other vciietablcs, i.« 

 greatly proiiioud bv the live and e.isv access of 

 the air; which strongly enforces iho necessity of 

 pulverizing and rendering the soil in a state of 

 considerable jincnes,-. iiofore they are iniroduccd 

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

 ture of the air, and in uater, sviihotil the inter- 

 vention of earth ; but neither of these is suiii- 

 eient for the puvpofe'without tlie free adniissi<;ii 

 of air. Man> j)l;'.ni4 of the suecuieni kind retain 

 their vegetative ipialitv a considerable Icn-jih of 

 time, merely by tiie asicncy of the air; and some 

 emit roots froni the bratiches that arc cut from 

 them, on being exposed to the air. without the 

 assistance of either eavih or water. The Scilinii 

 and Si-iiipirr:! iiin atloi.l exanijiles of this kind. 

 Air is likewise neccssar\- m order to preserve the 

 vegetative faculty of grains and i?cids vvliilc the)' 



