170 BOARD OF AGRICULTURE. 



treatment have made it one of the most valuable of agricultural 

 plants, yielding a juice with from twelve to fifteen per cent, 

 of cane-sugar. There is every reason to believe that the 

 flavors of fruits and the most desirable qualities of all the 

 vegetable products of the farm and garden may be thus im- 

 proved and controlled by the intelligent use of fertilizers, and 

 this consideration adds practical importance to the study of 

 vegetable physiology. We all know that whenever a hive of 

 bees find themselves without a queen or roj^al eggs they at 

 once proceed to develop a common egg into a royal larva by 

 feeding it with a peculiar food. Is it unreasonable to hope 

 that we may learn how to modify as radically the nature and 

 qualities of plants by a similar process ? 



The food of plants consists chiefly of carbonic acid gas, 

 and is absorbed from the air by the green parts, which, like 

 the leaves and young bark,' contain chlorophyl, and are 

 furnished with stomata. More than half the weight of ordi- 

 nary dry vegetable matter is thus derived from the atmosphere. 

 It may aid to fix this fact in mind, to consider that there is 

 constantly floating in the air, over every acre of the earth's 

 surface, seven tons of carbon which, if precipitated at once 

 as lampblack, would be likely to leave a permanent im- 

 pression. Yet the proportion of carbonic acid in the atmos- 

 phere is only one part in twenty-five hundred ])y measure. 

 The question naturally arises whether plants would not grow 

 faster if furnished with more of this food. Experiments 

 have shown that in sunshine they can digest a more concen- 

 trated carbonized air, but that such air exerts a deleterious 

 effect at all other times. 



Water is the most important of the remaining constituents 

 of ^lant-food, and in the liquid form is wholly absorbed by 

 the rootlets,, though aqueous vapor must under some circima- 

 stances be imbibed by other vegetable organs. The elements 

 of water, oxygen and hydrogen, are united with carbon in 

 the same proportion in which they exist in this fluid in the 

 living cells, principally of the leaf, to form the common ma- 

 terial of vegetable tissues called cellulose and several other 

 substances having nearly or precisely the same composition, 

 but difierent properties and uses. These are mainly starch, 

 gum, and several varieties of sugar, which, by the vital ac- 



