Mr Murray on the Physiology of the Root in Plants. 329 
nobler tree, but have no communication with the gross ingre- 
dients of the soil. 
The delicate vessels of the root are not suited to the absorp- 
tion of carbonaceous matter from the earth, and still less for ter- 
rene and metallic particles, ever found in the ashes of incinerated 
vegetable matter. It is only to gaseous bodies that such subtle 
structures can be supposed applicable ; and I infer from my ex- 
periments that such are excretory vessels, not absorbents. 
Silica and alumina serve a mechanical part in soils, and lime 
acts chiefly chemically, in decomposing the salts of iron, and 
animal and vegetable matter supplied as manure ; the gaseous 
bodies thus liberated escape gradually from the surface soil, and 
form a healthy atmosphere for the plant, by which it is decom- 
posed and assimilated, and forms the proximate or immediate 
principles of plants. 
Burnt clay and dry chopped (undecomposed) straw, are said 
to act as manures, but such can afford no nourishment to plants. 
The relations which earths bear to temperature, and to moisture, 
in their absorbent and retentive characters, should always be 
taken into the estimate, and the action of burnt clay may be ex- 
plained in this way. 
While in London, last winter, I made a considerable number 
of experiments on the hyacinth, &c. growing in bulb-glasses. 
The bulb, being carefully washed with distilled water, was seat- 
ed on the glass filled also with distilled water, and the whole 
covered with a bell-glass. In two or three days the water was 
highly saturated with carbonic acid gas, and this being precipi- 
tated with lime-water, potassa or caustic baryta, afforded a brisk 
effervescence on the affusion of diluted acid. The immediate 
milkiness which ensued on agitating the fluid with lime-water, 
was proof enough, though it was well to carry the experiment 
to its ultimatum. In numerous repetitions I found it uniform, 
and shewed it to some of my friends. 
By using lime-water, much diluted with distilled water, the 
interior surface and bottom of the bulb glass were encrusted 
with minute rombs of carbonate of lime, perfectly diaphanous. 
From a seedsman in Fleet-street, I got a bulb and bulb-glass; 
the roots had already shot down fibres into the water four to five 
inches long, and it was fast advancing into flower. The fibres 
