72 



HOW CROPS GKOW. 



has already appeared that the substances j list- described 

 stand very closely related to each other in chemical com- 

 position. In the following table their composition is ex- 

 pressed in formute. 



CHEMICAL FOKMUL^ OF THE CAKBHYDBATES. 



As above formulated, it is seen that all these bodies, 

 except arabinose, contain 6 atoms of carbon, or a num- 

 ber which is some simple multiple of 6, united to as much 

 hydrogen and oxygen as form in most cases 5, 6 or 11 

 molecules of water (HjO). Being thus composed of car- 

 bon and the elements of water they are termed Carhhy- 

 drates. 



The mutual convertibility of the carbhydrates is the 



* These soluble bodies when dried probably lose water which is 

 essential to their composition, as on drying they become insoluble. 



