40 BIOLOGY OF PLANTS. 



Mliller calls it organic assimilation, and this seems to accord 

 with the usage of biological writers. 



But whatever name physiologists may give to this power, 

 and whatever attempts they may make to analyze or define 

 the idea of life, whether we study it in the separate functions 

 of secretion, assimilation, or any other organic change, its 

 nature is wholly unknown to us. We know what its effects 

 and laws are, and can better understand them by conceiving, 

 as their cause, a peculiar poiar, essentially distinct from the 

 ordinary agents of dead matter, although producing both me- 

 chanical and chemical effects. 



But on the supposition that such a power exists, what influ- 

 ence can it exert upon the theory or practice of agriculture ? 

 In answer to this inquiry, it may be observed, 



1. That it is useful to have reference to the irital power , 

 in the whole process of tillage. Regarding this power as the 

 great agent in the process of vegetation, we may refer all the 

 productions of the farm to it as a cause. 



The science of tillage is a knowledge of those laws by which 

 the vital power is governed, and of the conditions which are 

 necessary to its activity ; and practical farming consists in 

 acting according to its laws, and in supplying those conditions 

 which are required for its most perfect development. 



I will illustrate the relation which the vittd power in plants 

 sustains to the science and practice of agriculture, by a refer- 

 ence to the science and practice of medicine. What is the 

 science of medicine? It is a knowledge of those laws which 

 govern the vital power, as it exists in the hunjan species, and 

 of those conditions which are necessary to the complete de- 

 velopment and perfection of this power, including, of course, 

 whatever may obstruct it in its operations. And what is the 

 practice of medicine? It is mainly concerned in applying 

 remedies to remove the obstacles to the proper action of vital- 

 ity ; a provision being made by our Maker in our appetites, 

 so that we become our own physicians, in supplying moi?t of 



