44 CHEMISTRY, GEOLOGY 



If a soil was wholly destitute of one of these 

 substances, it could not yield good crops ; and if 

 it contained an abundance of them all, with but 

 a single exception, and that found only in a very 

 small amount, plants which required only a very 

 small quantity of that substance would thrive 

 well on such soil ; but those which required a 

 large quantity of that substance of which the soil 

 contained only very little, would be stunted, un- 

 healthy, and unproductive. 



Suppose a piece of land contained only a small 

 quantity of lime, you will find, on looking at the 

 table of ashes, that rye grass, which contains 

 very little lime, would do well on that soil ; but 

 lucerne, which contains a great deal of lime, 

 would not be likely to thrive on land which con- 

 tains only a small quantity of that substance. 

 Rye grass would grow well on soil containing an 

 abundance of sand, but lucerne \\ould not so well. 

 Rye grass requires very little phosphoric acid in 

 the soil ; lucerne requires a much larger quan- 

 tity. 



Questions. What would be the result of a soil contain- 

 ing none of some one of these substances ? What would be 

 the result of soil containing plenty of all these substances, 

 with only a small quantity of some one of them ? Give an 

 illustration of the fact just named. 



