26 THE ALUMNI JOURNAL 



Most plants fail to produce chlorophyll in darkness, although some 

 do (conifers and maple). Light, especially the red rays, act as stimu- 

 lus. The work of chlorophyll cannot be done in darkness, nor can 

 protoplasm produce chlorophyll without it. Plants grown in the dark 

 or at low temperature are called "etiolated." They are of a yellowish 

 color, and turn green on exposure to light. The coloring matter 

 "etiolin" is most likely an intermediary substance in the formation 

 of chlorophyll and is changed into this substance upon absorption of 

 red light rays. 



Iron is not a constituent of chlorophyll, but it also seems to act as 

 a stimulus upon the living protoplasm to produce chlorophyll. On 

 the other hand, neither light nor iron alone can bring about the pro- 

 duction of chlorophyll. The cell must contain certain specific chromo- 

 plasts. The cells of animals, fungi and certain phaneroganic para- 

 sites do not contain these chromoplasts and do, therefore, not form 

 chlorophyll. 



As the presence of certain granules is necessary to form chloro- 

 phyll, so will chlorophyll do its work only when in the granule and 

 again then only when contained in the living protoplasmic cell. Iso- 

 lated chloroplasts continue for a time to absorbe COo and give off 

 oxygen. If anaesthesized by ether, they will only absorb light rays, 

 but no longer take up CO, nor give off oxygen. 



The conditions and factors necessary for the change taking place 

 in the cell are COo, HgO, warmth, light or definite wave length chlo- 

 rophyll and protoplasm. We might compare the cell to a factory. 

 Light is the stimulus which sets the machinery going. Water and 

 CO2 are the raw materials, chlorophyll is the machinery itself. Starch 

 is the food product turned out. 



How is this wonderful work accomplished ? Only very little is 

 known about it. 



As I stated before, starch is the first visible product of this photo- 

 synthetic process, but it is surely not the first and only product. The 

 starch molecule is very complex, carbon dioxide and water very simple 

 in chemical construction. We must assume, therefore, that a number 

 of simpler compounds are first formed and these again are changed 

 into starch. 



