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matters. Some, as Boussaingault, go so far as to regard the dark mucilaginous matters said to be 
exuded by roots in water as the effect of a diseased action, denying the excretion, hut this cannot be 
maintained, for amphibious plants as mints, cress, Myosotis palustris and other species, which are 
not placed in an abnormal situation when growing in water, yield this substance. The experiments 
of Gyde appear also explicit on this point. If we are to receive the theory of Dutrochet, that the 
penetration of the soil fluid through the roots is a phenomenon of Endosmosis, there is a necessity of 
admitting the passage outwards of a portion of the elaborated sap, which Gyde states to be identical 
in composition with the excrementitious matters collected by himself. That none should be obtained 
from sand, or soil, under certain circumstances, is not surprising, for the exposure of the exuded 
matter, over a large surface and in contact with oxygen absorbed from the air, would rapidly change 
it into a new body capable of escaping the ordinary tests—in the same way that alcohol by mere 
exposure over an extended surface is rapidly converted into acetic acid by oxydation. Although it 
is premature to deny that a portion of elaborated sap does escape from the root of some plants, it is 
very evident that this does not create a deposit injurious to the future growth of the species and is 
not the principle on which rotations are to be devised. 
The natural succession of plants is connected with the presence of organic matter in the soil. 
The richest weeds which first occupy the surface having the greatest necessity for it, and thus 
through successive groups to the grasses and forest trees which grow well without any portion in 
the soil. Other elements of fertility being present, the Chenopodiaceous and allied families thrive 
only in such localities as yield azotized matters, since they cannot grow without a supply from the 
soil. This surmise is sanctioned by the obvious presence of organic matters in the soils where they 
grow, and by the fact that some species exhale ammoniacal gases, but it is fully established by the 
experiments of Boussaingault. This chemist grew clover, peas, wheat and oats in a soil 
completely destitute of organic matter and supplied them with distilled water only; the clover and 
peas were found to double their azotized matter during growth, whilst the oats and wheat gained 
none whatever. As there was but one source of azote present, the atmosphere, it is apparent that the 
former have the capacity of supplying themselves therefrom, whilst the grain plants are altogether 
dependent on the soil. Hence in a soil charged with organic matters, rich in azote, those plants 
which require a supply by their roots will grow freely, and so far exhaust it in time as to render it 
unfit for the species, which is succeeded by an intermediate class, and finallyby the Gram blue, Legumi- 
nosee, and others capable of subsisting on aerial azote, and so far from exhausting, adding it to the soil. 
From this function of plants, we see an explanation of the natural rotation, and what is of more 
moment, a means of adapting our succession of crops to the accumulation as well as removal of 
azotized matters. 
