INTRODUCTION 45 



of the test-tube and displace the water. Thus in 

 time a test-tube of the gas may be collected. A 

 glowing chip will ignite if held in the test-tube, 

 showing that the gas collected is oxygen. In water 

 deprived of air there is no bubbling, even in the best 

 of light (Fig. 6). 



What happens when the chloroplasts are exposed 

 on one side to the light of the sun, which is a source 

 of energy, and on the other to the water of transpira- 

 tion, is that the carbon dioxide of the atmosphere 

 taken in combines with the water, and the action of 

 light upon the chlorophyll is that the latter takes 

 up some energy by photo-synthesis, and the chloro- 

 plast, by a process called assimilation or fixation, 

 builds up the carbon into starch or possibly cane- 

 sugar, and the first product is formaldehyde, CHoO, 

 and then sugar. During the process oxygen is 

 evolved. 



Thus, CO2 + HoO = CH3O + O2. 



It is then the chlorophyll which energises the 

 chloroplast which is the prime factor in this function. 



The starch grains occur in the chloroplastids, 

 showing clearly that the latter are the originators of 

 this organic compound. 



If placed in formaldehyde the chlorophyll is 

 extracted and the plastids remain. 



Engelmann showed that the red rays are the most 

 important in photo-synthesis and carbon fixation. 



The green, blue, and violet rays are little, if at all, 

 used. Certain bacteria will collect around a plant 



