Leaves and Their Work 139 



ide when the leaves have taken it up. As has been said, 

 in most plants nearly one-half the dry substance left when 

 the water is removed consists of carbon, of which char- 

 coal is an impure form. Carbon enters into the compo- 

 sition of every animal and vegetable substance, no matter 

 how minute. It is to be found in every part of a plant 

 from the root upwards, but especially in the seed. In 

 the grains which we use as food the quantity of carbon 

 amounts to some forty or fifty per cent of the whole; and 

 though the carbon compounds are not, like the nitrogenous 

 compounds, flesh-formers, they are equally important as 

 fat-formers, and as supplying fuel to maintain the heat of 

 our bodies. The carbon of our food is oxidized, burned, 

 by the oxygen of the air we breathe; heat is thus pro- 

 duced, and the greater part of the carbon is given back to 

 the air as carbon dioxide. 



One pound of wheat flour contains about nine and a 

 half ounces of starch, and starch is a compound of carbon, 

 oxygen, and hydrogen; but it also contains two ounces of 

 gluten — one of the nitrogenous compounds — and half of 

 this is carbon; and besides these it contains smaller quan- 

 tities of sugar, gum, and fat, and these are all carbon 

 compounds; so that altogether the pound of flour con- 

 tains some seven ounces of carbon. 



Some of the palms, as the sago palm, use very large 

 quantities of carbon in forming the starch of their pith: 

 one tree, for instance, often yielding the extraordinary 

 amount of eight hundred pounds of starch. All the 

 sugars, oils, gums, caoutchoucs, of the vegetable world, 

 contain large quantities of carbon, and so also do the 

 fibers of cotton, flax, hemp, and others. 



But as already said, carbon forms part of the struc- 



