MANURE. 139 



demand further what this means, we discover merely 

 that the excrements of men and animals are sup- 

 posed to contain an incomprehensible something 

 which assists in the nutrition of plants, and 

 increases their size. This opinion is embraced 

 without even an attempt being made to discover 

 the component parts of manure, or to become 

 acquainted with its nature. 



In addition to the general conditions, such as 

 heat, light, moisture, and the component parts of 

 the atmosphere, which are necessary for the growth 

 of all plants, certain substances are found to exer- 

 cise a peculiar influence on the development of 

 particular families. These substances either are 

 already contained in the soil, or are supplied to it 

 in the form of the matters known under the general 

 name of manure. But what does the soil contain, 

 and what are the components of the substances 

 used as manure ? Until these points are satisfac- 

 torily determined, a rational system of agriculture 

 cannot exist. The power and knowledge of the phy- 

 siologist of the agriculturist and chemist must be 

 united for the complete solution of these questions ; 

 and in order to attain this end, a commencement 

 must be made. 



The general object of agriculture is to pro- 

 duce in the most advantageous manner certain 

 qualities, or a maximum size, in certain parts or 

 organs of particular plants. Now, this object can 

 be attained only by the application of those sub- 



