Component Parts of the Soil on Vtgefalion. 77 



ment?. tliat. plants can live and grow in pure azote after the 

 iJrst expansion ot the germ, which is effected by the acces- 

 sion of oxvo-en, ha* taken place. 



Besides this proof chemists refer to a well-known and 

 instructisc experiment, that plants thrive exceedingly well 

 in willow earth* ; and they assert that this earth consists 

 of nothing else than hvdrooen, carbon, and oxvsfen, by 

 which thev endeavour to show that the vessels used in the 

 operation, and local and accidental causes, max- give occa- 

 sion to the existence of different kinds of earth in the resi- 

 dua, thoiiuh they acknowledge that there are plants which 

 contain among tlK.'ir component parts a great deal of pure 

 earth. 



From this mav be deduced the foHowing consequence; 

 that the requisites for promoting the gro-wth of plants, be- 

 sides light, heat, and atmospheric air, of which I do not 

 here ntcan to treat, are good mould, which is indispensably 

 necessarv, and vihieh is similar to the above-mentioned 

 willow earth, consistinii of matters in part dissolved by 

 putrefaction ; and it is certain that land will be productive 

 if covered with such mould to the depth of a furrow. But 

 this pure mould possesses chemical and mechanical proper- 

 ties, in consequence of w hich, supposing them to exist in 

 the mass, it cannot in manv places be either of long dura- 

 tion or useful. It is of a veiv tender texture, and therefore 

 indjibcs a great deal of water ; it however as readilv suffers 

 it to escape again, and with a moderate degree of drouoht 

 falls into dust, which is liable to be dispersed bv the wind ; 

 the water can extract from it the nourishing parts, and 

 where there is the least declivitv sweep it awav : its volume 

 in reirard to the organic bodies from which it is formed is 

 very small, ai»d a considerable quantity of organic bodies 

 arc necessary to constitute a moderate sized mass of such 

 tarth. 



But as the surface of our earth is fiill of inct^ualities from 

 which it cannot be freed, and as the putref\-ing organic 

 matter which can be found is not sufficient to supplv the 

 place of that washed awav by one shower of rain fj or bv 

 an inundation, it will be ?.ttended with advantage to mi* 

 other kinds of earth with the mould ; and experience shows 

 that it is only when organic bodies are in a state of putre- 



• The oak and beech produce the same kind of vegetable earth when 

 ihcir interior jmiTs have been dissolved by putrefaction. 



+ A great deal of wet weather in spring and harvest, say the firmer^ 

 drowns the fields, th-^t is to say, washes away and conies oxF the light 

 taluble carbonic "matter of the soil, 



faction. 



