FOOD OF PLANTS. 
525 
as it may be again diffused through water, or dissolved as it 
was before the evaporation. Saussure would lead us to be¬ 
lieve that plants obtain their earths from the soil ; for beans, 
supported by distilled water, yielded only one third of the 
quantity of ashes afforded by those grown in the soil; while 
those fed by rain-water gave little more than one half of the 
latter quantity. 
Thirty-two ounces of dry corn contained earths and me¬ 
tallic oxides as under— 
Wheat. 
Rye. 
Barley. 
Oats. 
Carbonate of lime . 
. 12 6 
13-4 
24 8 
33 75 
Silica .... 
. 132 
15 6 
66-7 
144-2 
Carbonate of magnesia . 
. 13-4 
142 
25-3 
33 9 
Alumina 
. 0-6 
1-4 
4-2 
45 
Oxide of manganese 
. 5-0 
32 
67 
6-95 
Oxide of iron 
. 25 
09 
3-8 
4-5 
One hundred parts of ashes lixiviated gave as under — 
Wheat . 
Barley . 
Oats 
Bear, or here 
Rye 
Potatoes 
Red clover 
Silex. 
Calx and 
Muriatic. 
Argil. 
48 
37 
15 
69 
16 
15 
68 
26 
6 
65 
25 
10 
63 
21 
16 
4 
66 
30 
37 
33 
30 
Schroeder seems to prove that a part of the earths must 
be derived from vegetation, even where plants are deprived 
of any opportunity of deriving fixed principles from the soils 
where they grow. He planted vegetables in sulphur and in 
the oxides of antimony and zinc, containing no earthy 
matter, and placed them in boxes, with free access of light 
and air, with dust and rain excluded, and fed them with 
distilled water. He found that the plants contained more 
earthy matter than the seed from which they grew, and 
which he had previously analysed and ascertained the consti¬ 
tuent parts. Plants growing in distilled water, and with 
free access of light and air, nearly doubled the portion of 
carbon they originally contained; but with little share of 
light, it was diminished from the latter quantity : and hence 
the plants must have derived nourishment from the air. But 
as they never perfect seeds, and soon decay, it is evident that 
air and water alone cannot support healthy and productive 
vegetation. Plants draw earthy matter from soils where no 
XXXII. 69 
