239 



LECTURE VI. 



Of 'Manures of vegetable and animal Origin. Of the 

 Manner in which they become the Nourishment of the 

 Plant. Of Fermentation and Putrefaction. Of the 

 different Species of Manures of vegetable Origin ; of 

 the different Species of animal Origin. Of mixed 

 Manures. General Principles with Respect to the 

 Use and Application of such Manures. 



THAT certain vegetable and animal substances 

 introduced into the soil accelerate vegetation and in- 

 crease the produce of crops, is a fact known since the 

 earliest period of agriculture \ but the manner in 

 which manures act, the best modes of applying them, 

 their relative value and durability, are still subjects of 

 discussion. In this Lecture* I shall endeavour to lay 

 down some settled principles on theee objects ; they 

 are capable of being materially elucidated by the re- 

 cent discoveries in chemistry ; and I need not dwell 

 on their great importance to farmers. 



The pores in the fibres of the roots of plants are 

 so small, that it is with difficulty they can be discovered 

 by the microscope 5 it is not therefore probable, that 

 solid substances can pass into them from the soil. I 

 tried an experiment gn this subject : some impalpa- 

 ble powdered charcoal procured by washing gunpow- 



