INTRODUCTION OF FERTILITY. 103 



of the plants. A fertile soil, cultivated so as to 

 exhibit its fertility in the most profitable manner, 

 has growing upon it crops whose habit and specific 

 character are adapted to the climate in which they 

 are placed, and to the character of the soil itself. 

 It yields these crops in the order in which each, 

 succeeding to the cultivation of its predecessor, shall 

 find the soil, chemically as regards its contents, 

 and mechanically as regards its texture, and practi- 

 cally as regards consequent cleanness of the land, 

 and the fitness of their respective times of cultiva- 

 tion to one another, in best condition for the supply 

 of the wants of the crop in question. It is annually 

 manured and cultivated so as best to meet the cur- 

 rent wants of the plants raised upon it ; but it is 

 especially dependent for all its powers to bring these 

 crops to a fruitful maturity upon the fact that there 

 is, during and after every shower of rain, a continual 

 current of water and of air passing throughout its 

 substance. This current should not be too rapid, 

 lest its soluble parts should be washed to water; 

 indeed, it is hardly possible that it should be too 

 slow; slow enough, however, to dissolve from the 

 soil whatever it contains of food for plants, and fast 

 enough to be continually bringing fresh supplies by 

 every mouth which the absorbing extremities of 

 the roots present. 



" All these purposes of warming the soil, of in- 

 troducing substances into it which shall operate 



