220 BULLETIN OF THE BUSSEY INSTITUTION. 
In this point of view, the common occurrence of sulphate of lime 
in natural waters manifestly supports the conception that the tendency 
of rain-water, which has often been noticed, to gradually wash out and 
remove lime from soils, is to be attributed primarily to the ready for- 
mation of soluble supercarbonate of lime in dry soils, and to the mo- 
bility of this solution. It may be true, indeed, that, because of this 
kind of leaching, many dry light soils may stand in greater need of 
calcareous manures, considered merely as plant food, than has been 
commonly supposed hitherto. ‘8 
It is not through the downward movements, alone, of the soil-water, 
that the influence of the soluble lime-carbonate should be estimated ; 
for, during the larger part of the summer season in our climate, the 
movement of water near tle surface of most cultivable soils is upward 
rather than downward. Excepting times when the ground is soaked 
by rains, a movement of moisture towards the surface of the soil is 
constantly determined by the capillary power of the soil, by evapora- 
tion from its surface, and by the pumping power of the roots of vege- 
tation, to supply the water needed for the exhalation of the leaves. 
But one result of this upward movement of the soil-water must be to 
bring the supercarbonate of lime toward the surface, where the lime- 
carbonate is probably often deposited in the insoluble form through 
evaporation both of the water and of the excess of carbonic acid. 
In corroboration of this idea, I have noticed, in numberless instances, 
in experiments upon the growth of buckwheat in glass jars filled with 
various soils and sands, that in the course of two or three months, a 
thin, firm crust of carbonate of lime is very apt to form upon the 
mouths of the jars, just above the surface of the earth. ‘This crust is 
insoluble in mere water, but dissolves readily, with effervescence, on 
being moistened with an acid; and the occurrence of the crust is so 
constant and general, in the experiments in question, that, in cleaning 
the jars after use, I long since adopted the practice of thrusting their 
mouths into muriatic acid for a few moments, after the insides of the 
jars had been washed with the acid, in order to be perfectly sure of 
the removal of the obnoxious crust. 
In like manner, Hallier* has noticed that flower-pots of porous 
earthenware, and the roots of plants grown in flower-pots, are often 
* “ Botanische Zeitung,” 1867, 25. 80; Compare Hoffmann’s “ Jahresbericht 
der Agrikultur-Chemie,” 1867, 10. 114. 
