71 
water plants speedily wither and die. It gives the soft parts 
that degree of succulence necessary for the performance of their 
functions; — it affords two elements, oxygen and hydrogen, 
which either as water, or under some other form, are contained 
in all vegetable products ; — and, lastly, the roots absorb from 
the soil those substances only, which are dissolved or suspended 
in water. So carefully, indeed, has nature provided against the 
chance of deficient moisture, that the leaves are endowed with a 
property both of absorbing aqueous vapour directly from the 
atmosphere, and of lowering their temperature during the night 
by radiation so as to cause a deposition of dew upon their sur- 
face, in consequence of which, during the driest seasons and in 
the warmest climates, they frequently continue to convey this 
fluid to the plant, when it can no longer be obtained in sufficient 
quantity from the soil. But necessary as water is to vegetable 
life, it cannot yield to plants a principle which it does not pos- 
sess. The carbonaceous matter which accumulates in plants, 
under the circumstances, above mentioned, may, with every ap- 
pearance of justice, be referred to the atmosphere; since we 
know that carbonic acid exists there, and that growing vegeta- 
bles have the property of taking carbon from that gas. 
113 Ashes OF Plants. When plants are incinerated, their ashes 
are found to contain saline and earthy matters, the .elements of 
which, if not the compounds themselves, are supposed to be de- 
rived from the soil. Such at least is the view deducible from 
the researches of Saussure, and which might have been antici- 
pated by reasoning on chemical principles. The experiments 
of M. Schrader, however, lead to a different conclusion. He 
sowed several kinds of grain, such as barley, wheat, rye, and 
oats, in pure flowers of sulphur, and supplied the shoots as they 
grew with nothing but air, light, and distilled water. On in- 
cinerating the plants, thus treated, they yielded a greater quan- 
tity of saline and earthy matters than were originally present in 
the seeds. These results, supposing them accurate, may be ac- 
counted for in two ways. It may be supposed in the first place, 
that the foreign matters were introduced accidentally from ex- 
traneous sources, as by fine particles of dust floating in the at- 
mosphere; or, secondly, it may be conceived, that they were 
derived from the sulphur, air, and water, with which the plants 
were supplied. If the latter opinion be adopted, we must infer 
136 AUCTARICM. U3, Dr. Turner's Elements of Chemistry. 
