S74 HOW CROPS FEED. 
point of remuneration, but the sterility thus induced is of 
a kind that easily y ‘elds to rest or other meliorating agen- 
cies, and is far from resembling in its permanence that 
which depends upon original poverty of constitution. 
Significance of the Absorptive Quality.—Disintegration 
and nitrification would lead to a waste of the resources 
of fertility, were it not for the conserving effect of those 
physical absorptions and chemical combinations and re- 
placements which have been described. The two least 
abundant ash-ingredients, viz., potash and phosphoric acid, 
if liberated by the weathering of the soil in the form of 
phosphate of potash, would suffer speedy removal did not 
the soil itself fix them both in combinations, which are at 
once so soluble that, while they best serve as plant-food, 
they cannot ordinarily accumulate in quantities destruct- 
ive to vegetation, and so insoluble that the rain-fall cannot 
wash them off into the ocean. 
The salts that are abundant in springs, rivers, and seas, 
are naturally enough those for which the soil has the least 
retention, viz., nitrates, carbonates, sulphates, and hydro-- 
chlorates of lime and soda. 
The constituents of these salts are either required by 
vegetation in but small quantities as is the case with chlo- 
rine and soda, or they are generally speaking, abundant 
or abundantly formed in the soil, so that their removal 
does not immediately threaten the loss of productiveness. 
In fact, these more abundant matters aid in putting into 
circulation the scarcer and less soluble ingredients of 
crops, in accordance with the general law established by 
the researches of Way, Eichhorn, and others, to the effect 
that any base brought into the soil in form of a freely sol-- 
able salt, enters somewhat into nearly insoluble combina- | 
tion and liberates a corresponding quantity of other bases. 
“The great bencficent law regulating these absorptions 
appears to admit of the following expression: those bodies 
which are most rare and precious to the growing plant are 
