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 result 

 with a proportionably smaller consumption of water. By increasing 

 the richness of the soil in soluble substances that can be assimilated, 

 Ave should succeed in economically reducing the quantity of Avater 

 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 Marie-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 

 symi^toms 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 abundance 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 Aveight 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. WoUny (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. 



