80 HOW CROPS GKO"W. 



decomposition, (Hoffmann, Quart. Jour. Chem. Soo., p. 

 767.) A kind of gum also appears in solutions of cane- 

 sugar or in beet-juice, when they ferment under certain 

 conditions. Inulin and the gums yield sugar, (levulose,) 

 but no dextrin, when boiled with weak acids. 



d. It will be noticed that while physical and chemical 

 agencies produce these metamorphoses in one direction, it 

 is only under the influence of life that they can be accom- 

 plished in the rcTcrse manner. 



In the laboratory we can only reduce from a higher, 

 organized, or more complex constitution to a lower and 

 simpler one. In the vegetable, however, all these changes, 

 and many more, take place with the greatest facility. 



The Chemical Composition of the Cellulose Group. — 

 It is a remarkable fact that all the substances just de- 

 scribed stand very closely related to each other in chemical 

 composition, while several of them are identical in this 

 respect. In the following table their composition is ex- 

 pressed in formulse. 



CHBMIOAl rOKMULiE OF THE BOTIIES OF THE CELLULOSE GROUP. 



Cellulose 

 Starch 

 iBulin 

 Dextrin 

 Bassorin 

 Veg. MiioUage 

 Metarabic acid 

 Arabic acid 

 Cane sugar 

 Fruit sugar 

 Grape sugar 



It will be observed that all these bodies contain 12 

 atoms of carbon, united to as much hydrogen and oxygen 

 as form 10, 11, or 12 molecules of water. 'We can, there- 

 fore, conceive of their conversion one into another, with 

 no further change in chemical composition in any case, 

 than the loss or gain of a few molecules of water. 



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