80 “HOW CROPS GROW. 
o 
decomposition, (Hoffmann, Quart. Jour. Chem. Soc., p. 
767.) A kind of gum also appears in solutions of eane- 
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 reverse 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 formule. ; 
CHEMICAL FORMULZE OF THE BODIES OF THE CELLULOSE GROUP, 
Cellulose 
Starch 
Inulin 
Dextrin C12 Heo O10 
Bassorin 
Veg. Mucilage 
Metarabic acid 
Arabic acid i 
Cane sugar i Cra Ha Ons 
Fruit sugar 
Grape sugar ; Cia Has Ora 
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. 
