accumulate in the plant, which probably perspires 
only absolutely pure water. 
In 1801 I made an experiment on the growth of 
oats, supplied with a limited quantity of distilled 
water in a soil composed of pure carbonate of lime. 
The soil and the water were placed in a vessel of 
iron, which was included in a large jar, connected 
with the free atmosphere by a tube, so curved as to 
prevent the possibility of any dust, or fluid, or solid 
matter from entering into the jar. My object was 
to ascertain whether any siliceous earth would be 
formed in the process of vegetation ; but the oats 
grew very feebly, and began to be yellow before 
any flowers formed : the entire plants were burnt, 
and their ashes compared with those from an equal 
number of grains of oat.. Less siliceous earth was 
given by the plants than by the grains ; but their 
ashes yielded much more carbonate of lime. That 
there was less siliceous earth, I attribute to the cir- 
cumstance of the husk of the oat being thrown off* 
in germination; and this is the part which most 
abounds in silica. Healthy green oats, taken from 
a growing crop, in a field of which the soil was a 
fine sand, yielded siliceous earth in a much greater 
proportion than an equal weight of the corn artifi- 
cially raised. 
The general results of this experiment are very 
much opposed to the idea of the composition of 
the earths, by plants, from any of the elements 
found in the atmosphere, or in water ; and there 
are other facts contradictory to the idea. Jacquin 
states that the ashes of Glass Wort ( Salsola soda), 
when it grows in inland situations, afford the vege- 
