THE DETERMINING FACTORS IN PHOTOSYNTHESIS 43 



noted by Agamaov (1927). Kostychev has also noted that even 

 with plenty of light and carbon dioxide, the plant may suddenly 

 stop manufacturing food for a short time and then resume opera- 

 tions again. This brief cessation, like the drop in the afternoon, 

 may be associated with some internal factor connected with the 

 photosynthetic machinery. Because smoke does not continuously 

 pour out of the chimney, however, is not an absolute proof that 

 the factory has shut down or stopped operations. 



Summary. — If one wished to make a corn plant produce the 

 maximum amount of carbohydrate in a given period of time, 

 the following favorable conditions would have to be provided: 

 (1) See that the plants maintain a healthy rich green color. (2) Pro- 

 vide abundant water. (3) Artificially maintain a temperature of 

 about 35° C. (4) Illuminate the plant continuously with light of 

 the optimum intensity. (5) Increase the carbon dioxide content 

 of the air to at least 1%. Ordinarily both light and temperature 

 are below the optimum but with a limited amount of carbon 

 dioxide at the disposal of the plant, light and temperature are not 

 limiting factors. 



QUESTIONS 



1. Are there any plants which lack leaves? If so, how do they manage 

 to live? 



2. Why do potato beetles affect the size of the crop? 



3. Is carbon dioxide more soluble in warm or cold water? What bearing 

 does this have upon life in Arctic regions? 



4. Parasitic plants are not green. Explain. 



5. How are celery plants "bleached"? Explain. 



6. Why are plants commonly placed in an aquarium? 



7. Frequently the lower leaves of a plant have longer petioles than the 

 upper ones. Why? 



8. Which are generally bigger, opposite or alternate leaves? Why? 



9. Can a lawn be maintained best under elms or maples? Why? 



10. In what part of a tree are the leaves borne? Why? 



11. Is it ever advantageous to a plant to be heliophobous during a part of 

 its life and heliophilous during another? Illustrate. 



12. When do wild flowers on the deciduous forest floor usually blossom? 

 Why? 



13. In which month do plants grow fastest? Why? 



14. On the Newfoundland Banks the catch of fish is said to be bigger in 

 sunny seasons than in cloudy ones. Why? 



15. Who first showed that the carbon of plants comes from the air rather 

 than from the soil? 



