114 
tain in unequal quantities soluble and nourishing principles the 
water absorbed by the roots may be more or less charged with these 
elements. We can understand, then, that the quantity of water 
necessary to enable a plant to furnish a given result is not the same 
for all soils, and that the richest soils may produce a greater yesult 
with a proportionably smaller consumption of water. By increasing 
the richness of the soil in soluble substances that can be assimilated, 
we should succeed in economically reducing the quantity of water 
consumed by the crops. In any case we might at the same time ask 
ourselves if all the water absorbed by the roots and introduced into 
the plant is utilized by it and at what limit the richness of the water 
should be arrested so as to be really profitable to the plant. In this 
connection Marié-Davy cites the following fact, mentioned by Perret 
in the Journal of Practical Agriculture for 1873: 
In Perret’s experiments a meadow having been covered with a suffi- 
cient quantity of nitrate of soda for a nitrogenous manuring of four 
years, the grass was magnificent in the spring. This grass was given 
green to the horses, who before long began to show strong diuretic 
symptoms accompanied by raging thirst. These animals seemed to 
be completely under the influence of the administration of a strong 
dose of nitrate. The following year there was a complete cessation 
of the beneficial effects of the nitrate on the meadow, which showed 
conclusively that the plants of the first year contained nitrate in a 
natural state and not decomposed by the assimilation. 
When nutritive substances are given to plants in abundané they 
can absorb a quantity of these elements besides what is necessary for 
their nourishment. This is particularly true when in the series of 
minerals which compose a normal nourishment, one of these sub- 
stances is in excess of the others. Besides, if we compare the chemical 
composition of a crop cut green with that of a similar crop after 
arriving at maturity, we find that in the latter there is a diminution 
in weight of several of the substances present in the former. It 
would, therefore, have been interesting to know if the trouble men- 
tioned by Perret was continued with the same intensity in the dry hay. 
RELATION OF PLANTS TO MOISTURE OF SOIL. 
E. Wollny (1887, Vol. X, p. 320) gives some results as to the influ- 
ence of plants and shade on the moisture of the soil, being a modifica- 
tion of a memoir published by him in 1877. His conclusions are as 
follows: 
(1) The water contained in the soil under a covering of living 
plants is, during the growing season, always less than in a similar 
layer of fallow, naked soil. 
