94 LESSONS IN CHEMISTRT. 



and water, you have seen, supply plants with some of the most 

 essential ingredients of their food, it is therefore important 

 that the soil in which they are fixed, should possess that 

 texture best adapted to allow the air and rain freely to 

 penetrate to their roots. It is not, however, sufficient that a 

 soil be loose and open, it must, at the same time, possess that 

 degree of consistence which will aflford plants a firm support. 

 So far as its physical qualities are concerned, "the most 

 productive soil is that which is so constituted as to maintain 

 such a degree of moisture in very diy and in very wet sea- 

 sons, as only to give a healthy supply of it to the plants. 

 Such a soil gives to plants the means of fixing their roots 

 sufficiently deep to support them during the period of their 

 growth, and allows them to ramify in every direction in 

 search of nourishment, where they may easily abstract the 

 elements of vegetable life without being injured by a redundant 

 or a deficient supply of moisture, during any period of theii* 

 growth." — {Morton.) Though the physical qualities of a 

 soil, and the proportions of sand-clay and vegetable matter 

 which it contains, its elevation above the sea, and its depth, 

 have, as the experienced farmer knows, an important influence 

 upon its fertility, yet " a soil," as the chemist Sprengel, the 

 head of the Prussian agricultural school, says, " is often 

 neither too heavy nor too light, neither too wet nor too dry, 

 neither too cold nor too wann, neither too fine nor too coarse, 

 lies neither too high nor too low, is situated in a propitious 

 cUmate, is found to consist of a well-proportioned mixture of 

 clayey and sandy particles, contains an average quantity of 

 vegetable matter, and has the benefit of a warm aspect and 

 favouring slope ; and is, notwithstanding all these advantages 

 unproductive, because it does not contain the chemical ingre- 

 dients which plants reqydre for their nourishment^ An 

 inspection of the analyses of the rocks from which the soils of 

 this country are derived, will show you that they are capable 

 of supplying these chemical ingredients in very different 

 proportions, and will also convince you that the only certain 

 method of estimating the agricultural capabilities of any 

 particular soil, is by acquiring a knowledge of its chemical 

 composition. 



