ASSIMILATION OF HYDROGEN. 63 



Plants do not, however, attain maturity, under 

 ordinary circumstances, in charcoal powder, when 

 they are moistened with pure distilled water instead 

 of rain or river water. Rain water must, therefore, 

 contain within it one of the essentials of vegetable 

 life ; and it will be shown, that this is the presence of 

 a compound containing nitrogen, the exclusion of 

 which entirely deprives humus and charcoal of their 

 influence upon vegetation. 



ON THE ASSIMILATION OF HYDROGEN. 



The atmosphere contains the principal food of 

 plants in the form of carbonic acid, in the state, 

 therefore, of an oxide. The solid part of plants 

 (woody fibre) contains carbon and the constituents 

 of water, or the elements of carbonic acid together 

 with a certain quantity of hydrogen. We can con- 

 ceive the wood to arise from a combination of the 

 carbon of the carbonic acid with the elements of 

 water, under the influence of solar light. In this 

 case, 72*35 parts of oxygen, by weight, must be 

 separated as a gas for every 27*65 parts of carbon, 

 which are assimilated by a plant. Or, what is 

 much more probable, plants, under the same cir- 

 cumstances, may decompose water, the hydrogen 

 of which is assimilated along with carbonic acid, 

 whilst its oxygen is separated. If the latter change 

 takes place, 8*04 parts of hydrogen must unite with 

 100 parts of carbonic acid, in order to form woody 



