36 THE CULTURE OF FARM CROPS. 



the relative weights in which the organic elements enter in- 

 to combination in all the vegetable products which are 

 grown for the support of animal life. 



All vegetable products contain some inorganic matter 

 which remains behind in the form of ashes when the plants 

 are consumed by fire, or as dust when they aro entirely de- 

 composed and reduced by decay. In both cases, when these 

 operations are entirely completed, the results are exactly 

 the same. This inorganic remnant varies considerably; 

 oats leaving but 4 per cent.; while ripe hay leaves 10 per 

 cent.; but each variety of plant contains a certain propor- 

 tion cf inorganic matter which is pretty nearly constant 

 and is peculiar to itself. These facts are exceedingly im- 

 portant in the practice of agriculture, and are simply no- 

 ticed here, coming hereafter under special consideration 

 when the nature of soils and the food for plants are under 

 discussion. 



After having studied the character of the organic elements 

 it will appear very clearly that they will not enter into the 

 substance of plants in their natural state, or as they exist 

 free and uncombined with other elements. Carbon is a solid 

 substance and is not soluble in water ; and as plants cannot 

 take up anything that is solid into their circulation and tis- 

 sue, but only matter that is dissolved in water, or which is 

 mixed with it in a gaseous form, or is in a free gaseous 

 state, it is clear that plants cannot derive their carbon di- 

 rectly from the element itself, as it exists in nature. Hydro- 

 gen does not occur in the soil or in the atmosphere in a free 

 state in any appreciable quantity, and in its simple condi- 

 tion cannot form any part of the food of plants. Oxygen 

 and nitrogen exist in the atmosphere in well known propor- 

 tiens, in a gaseous state, and the former is absorbed or in- 

 haled under certain conditions by the leaves of plants, while 

 it is quite possible that nitrogen may also be absorbed in 

 the eanie manner. But while it is known that oxygen is 

 taken up by the leaves, there is no knowleelge that nitrogen 

 is ; but every reascn to believe that it is not. These two 

 gases are slightly soluble in water and may occasionally be 



