328 HOW CROPS FEED. 
of the crops, and subtracting from that sum the ash of 
the seeds, together with the matters made soluble in the 
same soils, which had sustained no plants, but which had 
been treated otherwise in a similar manner. 
MATTERS DISSOLVED BY ACTION OF ROOTS. 
On 9 lbs. of On 11 lbs. of . 
sandstone. basalt. 
Of -S:lupin, plants 20.0603 26-0602 bee esse 0.608 oo. 0.749 grams. 
“3 pea Sennen ts ob ooh us preys 0.481 0:.TAB 
Ge = a a POE oer et 0.268 ‘ 0.565 ‘ 
Pe OUMECEIVIL G9. 2. tras avictcabe ood 0.232 * 0.327 “ 
POR Werem <i eh Saks: were teense O22 0.251 “ 
ae AG OP eas sin od me eee eeu 0,027.3 0.196. ** 
ot ae rye Sohn sh Rane wee ages 0.014 * 0.182 .-%* 
These trials appear to show conclusively that plants 
exert a decided effect on the soil. We are not informed, 
however, what particular substances are rendered soluble 
under this influence. 
We conclude, then, that the direct action of the roots 
of a crop may in all cases contribute toward supplying it 
with food, and in many instances may be absolutely 
essential to its satisfactory growth. 
Further Notice of Matters Soluble in Water.—The 
analyses we have quoted show that every chemical ele- 
ment of the soil may pass into aqueous solution. They 
also show that some substances are dissolved more easily 
and in greater quantity than others. 
In general, chlorine, nitric acid, and sulphuric acid, 
are most readily and completely taken up by water, and, 
for the most part, in combination with dime, soda, and, 
magnesia. In some cases, sulphuric acid appears to exist 
in a difficultly soluble condition (Van Bemmelen, Vs. 
St., VIIL, 263). 
Potash, ammonia, oxide of iron, alumina, silica, and 
phosphoric acid, are the substances which are usually 
soluble in but small proportion. These, together with 
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