212 THE PHENOMENA OF MOTION 



resistance to the tendency of the oxygen to combine 

 with some element of the living part, because its 

 power of resistance has been taken away by some 

 other application of its excess of vital force. Ac- 

 cording to the amount of oxygen brought to it, a 

 certain proportion of the living part would lose its 

 condition of vitality, and take the form of a che- 

 mical combination, having a composition different 

 from that of the living tissue. In a word, there 

 would occur a change in the properties of the living 

 compound, or what we have called a change of 

 matter. 



If we reflect that the capacity of growth or 

 increase of mass in plants is almost unlimited ; that 

 a hundred twigs from a willow tree, if placed in the 

 soil, become a hundred trees ; we can hardly enter- 

 tain a doubt, that with the combination of the ele- 

 ments of the food of the plant so as to form a part 

 of it, a fresh momentum of force is added in the 

 newly formed part to the previously existing mo- 

 mentum in the plant ; insomuch, that with the in- 

 crease of mass, the sum of vital force is augmented. 



According to the amount of available vital force, 

 the products formed by its activity from the food 

 are varied. The composition of the buds, of the 

 radical fibres, of the leaf, of the flower, and of the 

 fruit, are very different one from the other ; and 

 the chemical force by which their elements are held 

 together is very different in each of these eases. 



Of the non-azotised constituents of plants we 



