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turnips, but will not bear clover. What is the reason that a 
field loses its fertility for one plant, the same which at first 
flourished there ? What is the reason one kind of plant 
succeeds in a field where another fails ? ” 
“ These questions belong to science. What means are 
necessary to preserve to a field its fertility for one and the same 
plant ? — what to render one field fertile for two, for three, for 
all plants ? ” 
“These last questions are put by art, but they cannot be 
answered by art. If a farmer, without the guidance of just 
scientific principles, is trying experiments to render a field 
fertile for a plant, which it otherwise will not bear, his prospect 
of success is very small. The most exact observations prove 
that the method of cultivation must vary with the geognostical 
condition of the subsoil. In basalt, gray wacke, porphyry, sand- 
stone, limestone, &c., are certain elements indispensable to the 
growth of plants, and the presence of which renders them fertile. 
This fully explains the difference in the necessary methods of 
culture for different places; since it is obvious that the essential 
elements of the soil must vary with the varieties of composition 
of the rocks, from the disintegration of which they originated.” 
“Wheat, clover, turnips, for example, each require certain 
elements from the soil ; they will not flourish where the appro- 
priate elements are absent. Science teaches us what elements 
are essential to every species of plants by an analysis of their 
ashes. If therefore a soil is found wanting in any of those 
elements, we discover at once the cause of its barrenness, and 
its removal may now be readily accomplished.” 
“In the effects of time, in what in agriculture are technically 
called fallows — the repose of the fields — we recognise by science 
certain chemical actions, which are continually exercised by the 
elements of the atmosphere upon the whole surface of our globe. 
By the action of its oxygen and its carbonic acid, aided by water, 
rain, changes of temperature, &c., certain elementary consti- 
tuents of rocks, or of their ruins, which form the soil capable of 
cultivation, are rendered soluble in water, and consequently 
become separable from all their insoluble parts. By their 
influence the necessary elements of the soil become fitted for 
assimilation by plants ; and it is precisely the end which is 
obtained by the mechanical operations of farming. They accel- 
330. AUCTABICU. 
