IIECAPITULA^N OF FACTS. 25 



more than half is phosphoric acid, and there is scarcely 

 any silica. When we come to consider the purposes 

 for which these parts are intended, the cause of such 

 variations will be plainly perceived. We even find in 

 many plants a distinction between the composition of 

 the ash at the bottom of the stalk, and that at the top. 

 In all cases the ash from the husk which covers the 

 seed, as in oats, barley or buckwheat, differs exceed 

 ingly in its constitution from that of the seed itself. 

 We shall in subsequent chapters see what is the cha 

 racter of this difference, and understand at least a part 

 of the reasons for it. 



We have now called attention to several valuable 

 facts respecting the inorganic part or ash of plants : 



1. All of the inorganic substances described are 

 generally present in our cultivated crops, but not in 

 variably : sometimes one or two are absent. 



2. The quantity of ash yielded by different plants 

 varies. 



3. The composition of this ash also varies, and in 

 as great a degree as the quantity. 



4. This applies not only to different kinds of plants, 

 but to different parts of the same plant. 



Upon these four points depend many of the most 

 important discoveries in agriculture, and we shall find 

 them connected very intimately with all of the leading 

 subjects which are yet to engage our attention. Let 

 the reader, then, before proceeding farther, understand 

 them thoroughly and impress them upon his memory. 



