176 
other part which had dropped off during the course of vegeta- 
tion. On submitting each part to a chemical analysis, he 
found that the quantity of carbon which it contained, was some- 
what less than the quantity which existed in the bulb, or the 
seed from which the plant had sprung. 
These experiments have been repeated by Saussure with a 
very different result. Sprigs of mentha piperita, allowed to 
vegetate for some time in distilled water, nearly doubled the 
portion of carbon which they originally contained ; but when 
the same experiment was repeated in a place where but little 
light had access, the carbon, instead of being increased, was 
somewhat diminished, has Hassenfratz had found. Hence, it 
is possible that the result obtained by Hassenfratz was owing 
to the want of light. Thus it cannot be doubted, lliat plants, 
even when they vegetate in pure w ater, are capable of absorb- 
ing nourishment from the air; but as plants in this situation 
cannot produce perfect seeds, and as they gradually decay and 
cease to vegetate, it is obvious that water and air alone are not 
sufficient.” 
179 Soil INDISPENSABLE TO Vegetation. “ The third, and only 
remaining source from which plants can draw their food, is 
the soil on which they grow. Now this soil consists of two 
parts; namely, pure earths, which constitute its basis, and the 
remains of animals and vegetables applied as manure. One 
use of the earthy part of the soil is to furnish a support for 
the plants, and to administer the proper quantity of water to 
them ; but as all plants contain earthy and saline matters, and 
as these substances are constantly present, w e cannot avoid con- 
sidering them as in some measure constituting an essential part 
of plants. Now there is reason to believe that the proportion 
of earthy and saline matters in plants is considerably influenced 
by the soil on which they vegetate. Saussure made beans grow 
in three different situations. The first set was supported by 
distilled water; tlie second was planted in sand and supported 
by rain water; the third was planted in a pot filled with mould 
and placed in a garden. The ashes yielded by these different 
plants were to each other in the following proportions: — 
1 Those fed by distilled water . 3.9 
2 Those fed by rain water, . 7.5 
3 Those growing in soil . 12.0 
