INTRODUCTION 21 
quainted with. The gist of agricultural chemistry with 
_ him was, that plants are “‘ composed of gases with a smali 
proportion of calcareous matter;” for “although this 
discovery may appear to be of small moment to the prac- 
tical farmer, yet it is well deserving of his attention and 
notice, as it throws great light on the nature and food of 
vegetables.” The fact being then known that plants ab- 
sorb carbonic acid from the air, and employ its carbon in 
their growth, the theory was held that fertilizers operate 
by promoting the conversion of the organic matter of the 
soil or of composts into gases, or into soluble humus, 
which were considered to be the food of plants. 
The first accurate analysis of a vegetable substance was 
not accomplished until 15 years after the publication of 
Dundonald’s Treatise, and another like period passed be- 
fore the means of rapidly multiplying good analyses had 
been worked out by Liebig. So late as 1838, the Gittingen 
Academy offered a prize for a satisfactory solution of the 
then vexed question whether the ingredients of ashes are 
essential to vegetable growth. It is, in fact, during the last 
30 years that agricultural chemistry has come to rest on 
sure foundations. Our knowledge of the structure and 
physiology of plants is of like recent development. 
What immense practical benefit the farmer has gathered 
from this advance of science! The dense populations of 
Great Britain, Belgium, Holland, and Saxony, can attest 
the fact. Chemistry has ascertained what vegetation ab- 
solutely demands for its growth, and points out a multitude 
of sources whence the requisite materials for crops can be 
derived. To be sure, Cato and Columella knew that ashes, 
bones, bird-dung and green manuring, as well as drain- 
age and aeration of the soil, were good for crops; but 
that carbonic acid, potash, phosphate of lime, and com. 
pounds of nitrogen, are the chief pabulum of vegetation, 
they did not know. They did not know that the atmos. 
phere dissolves the rocks, and converts inert stone into 
