REASONS OF BARRENNESS. 63 



know what to do, but may not in all cases be able to 

 do it with a profit, and this with a practical man is 

 always an important distinction. 



It will be noticed in table first, that alumina, a 

 substance rarely, if ever, present In the ash of plants, 

 is quite an abundant constituent of soils. This is one 

 distinction between the inorganic part of plants and 

 that of the soil, alumina being a characteristic of the 

 one and absent from the other. In nearly ail soils, silica 

 is the leading substance, usually constituting fully 

 nvo-thirds of their whole weight, and often eighty or 



nety pounds in every hundred. The only cases in 

 , lk ioh it is not largely present are those of the pect 

 oogs, made up almost entirely of vegetable matter. 

 Silica forms compounds with certain of the other 

 bodies in the soil, making what are called soluble 

 silicates. The gradual formation of these compounds 

 affords a supply for the plant. 



We have now mentioned the substances which are 

 present in the soil, and have in a previous chapter 

 dwelt upon those which constitute the plant. Sundry 

 points of connection between the two, will already 

 have suggested themselves to the reader or student. 

 To these we must next turn our attention, in treating 

 of the various methods proper to be employed in 

 bringing soils to a state of fertility, and to a condition 

 the most easy and profitable for cultivation. 



From examining table first, and from the explana- 

 tions already given, it will be perceived that there 

 are various points to be considered in attempting the 

 improvement of a soil. a. If there be a chemical 

 deficiency, that is an absence of certain constituents 

 necessary to fertility, as mentioned above, then but 

 one course can be adopted with any hope of success: 

 this course is obviously to supply what is wanting. 

 The ways of doing this in the most advantageous and 

 economical manner, will be considered under w T hat 



