130 



BIOLOGY 



It must not be understood that this equation is an accurate, 

 statement of what occurs, for we do not know the details of the 

 building of starch from carbon dioxid. There is no doubt that 

 the process is far more complex than is. indicated by this simple 

 equation. The building of CO 2 and H 2 O into starch is not done 

 by a single step as here represented, but in all probability by 

 several steps. Moreover, the starch molecule is by no means a 

 simple molecule as the formula C 6 Hi O 5 indicates, but some 

 multiple of this formula; how high a multiple we do not know, 

 but probably with many times this number of atoms in the 

 molecule. The above equation represents the ratio of the atoms 



but not their actual number. While 

 the details of the method by which the 

 complex molecule of starch is formed 

 are not yet known to us, we do know 

 that the essential features represented 

 by this equation namely, that C0 2 

 and H 2 O are combined, that starch is 

 manufactured, and that oxygen is set 

 free are in the main correct. This 

 process is called photosynthesis (Gr. 

 photos = light + synthesis = composi- 

 tion), and it is the only known method 

 by which starch can be manufactured, 

 chemists having hitherto been unable 

 to make it by any artificial means. 



From the above equation it will be 

 seen that while carrying on photosyn- 

 thesis, a plant is using up carbon dioxid 

 and at the same time liberating oxygen 

 and producing starch. The oxygen is 

 liberated in the form of a gas which 

 passes from the plant into the atmos- 

 phere. The liberation of oxygen may be easily demonstrated 

 by placing some kind of green water plant in a dish of water 



FIG. 67 



Showing a method of demon- 

 strating that a plant while grow- 

 ing eliminates oxygen gas. The 

 plant is a green water plant, and 

 the bubbles which arise from it 

 and collect in the tube prove to 

 be oxygen. 



