70 Practical Farming 



woody material for trees. The only part of the plant con- 

 taining nitrogen is the living matter or protoplasm, which 

 does all the work of the plant. We find, then, in all our 

 food crops these two classes of substances : the nitrogenous 

 or proteid materials and the carbohydrates and fats. Of 

 these and their nature we will treat in another lesson. 



Take a large plant of green Indian com 

 How Plants ^^^ ^^^ j^ ^^^ ^g- j^ j^^ 'Phgj^ ^^y j^ 



Get Food , , , , .^ . , 1 1 . 



from the Soil thoroughly by artificial heat so as to drive 



off all the water. Weigh it again, and you 



will find that it has lost a great deal by parting with the 



water it contained. Now bum it. Bum it thoroughly, 



as a chemist would in a crucible, till nothing is left but 



pure white ash. With the exception of the nitrogen and 



water which has been driven off into the air, this little 



handful of ashes contains all that the plant took from the 



soil, and you can realize how small a portion of the bulk 



of the plant came from the soil. The ashes contain the 



lime, phosphorus, potassium, and other mineral elements. 



You have destroyed the stalk of corn as a stalk of corn, 



but you have not really destroyed anything. You have 



simply changed to another form of energy the energy of 



position located there by the sunlight acting on the green 



leaves. Thus in burning coal we get back the radiant 



energy of the sunlight of long ages ago when the plants 



that formed the coal-beds grew; and we send back to the 



air the materials that in the first place came from the air, 



the carbon dioxide and the water, so that nature can begin 



to use them over again in the construction of other plants. 



We can change the form of matter but we can never 



destroy anything. 



