70 
place during the night, bearing no considerable ratio to the de- 
gree in which the opposite effect occurs by day. He accounts 
for the discordance between his own results and those of Mr. 
Ellis, by his having carefully removed the plants from the ex- 
perimenting jar immediately they began to suffer from the heat 
or confinement, and conducted the experiments on a larger and 
more suitable scale. 
112 Food of Plants. The chief source from which plants de- 
rive the materials for their growth, is the soil. However various 
the composition of the soil, it consists essentially of two parts, 
so far as its solid constituents are concerned. One is a certain 
quantity of earthy matters, such as siliceous earth, clay, lime, 
and sometimes magnesia; and the other is formed from the re- 
mains of animal and vegetable substances, which, when mixed 
with the former, constitute common mould. A mixture of this 
kind, moistened by rain, affords the proper nourishment of 
plants. The water, percolating through the mould, dissolves 
the soluble salts with which it comes in contact, together with 
the gaseous, extractive, and other matters which are formed du- 
ring the decomposition of the animal and vegetable remains. 
In this state it is readily' absorbed by the roots and conveyed as 
sap to the leaves, where it undergoes a process of assimilation. 
But though this is the natural process by which plants obtain 
the greater part of their nourishment, and without which they 
do not arrive at perfect maturity, they may live, grow, and even 
increase in weight, when wholly deprived of nutrition from this 
source. Thus in the experiment of Saussure, already described, 
sprigs of peppermint were found to vegetate in distilled water; 
and it is well known that many plants grow when merely sus- 
pended in the air. In the hot-houses of the botanical garden of 
Edinburgh, for example, there are two plants, species of the fig 
tree, the ficus australis and ficus elastica, the latter of which, 
as Dr. Graham asserts, has been suspended for ten, and the for- 
mer for nearly sixteen years, during which time they have con- 
tinued to send out shoots and leaves. Before scientific men 
had learned to appreciate the influence of atmospheric air on 
vegetation, the increase of carbonaceous matter, which occurs 
in some of these instances, was supposed to be derived from 
water, an opinion naturally suggested by the important offices 
performed by this fluid in the vegetable economy. Without 
108 to 112 from Dr. Turner’s Elements of Chemistry. 
