304 PLANT PHYSIOLOGY 



Amount of Enzymes. — Since respiration is dependent upon the 

 presence of enzymes, their amount is closely correlated with 

 respiratory activity. They are dependent for their formation 

 upon the presence of water and the presence of protoplasm, which 

 explains in part the relation which these two substances bear to 

 respiration. The fact that enzymes act only in a medium of a 

 specific acidity will also explain in part the effect of acids and alka- 

 lies on respiration. In fact most of the conditions enumerated 

 above affect respiration either through their influence upon the food 

 supply or through their effect upon the formation and activity 

 of the necessary enzymes. 



QUESTIONS 



1. Why do plants die when the soil is flooded? 



2. What are lenticels? 



3. Why are the peduncles and petioles of water lilies hollow? 



4. Iljin reports that the first effect of drouth is to increase respiration. How 

 may this be explained? 



5. Just when in plant metabolism does the potential energy of the food 

 become kinetic? 



6. If a plant were grown in air freed of oxygen, would it live longer in the 

 dark or in the light? 



7. What does the increase in dry weight in a plant actually measure? 



8. Why were the plants of the coal measures preserved? 



9. Which weighs more per unit volume, — sound wood or decayed wood? 

 Why? Which gives more heat when burned? 



10. Why are flowerpots generally unglazed? 



11. Name three advantages gained by plowing. 



12. What causes black heart of potatoes? 



13. Why do succulents like the agave and cacti find a reserve of carbon 

 dioxide in the form of organic acids of especial survival value? 



14. Maquenne and Demoussy reported that they had kept Aucuba alive in a 

 vacuum in diffuse light for more than a year. How is this possible? 



15. What is phosphorescence and its relation to respiration? Why has it not 

 been discussed more fully in this text, dealing chiefly with the physiology of the 

 Spermatophytes? 



REFERENCES 



Andrews, F. M. — The effect of aeration on plants. Proc. Ind. Acad. Sci., 

 1921:147. 



Hopkins, E. F. — Variation in sugar content in potato tubers caused by wound- 

 ing and its possible relation to respiration. Bot. Gaz., 84:75, 1927. 



Hover, J. M., and Gustafson, F. G. — Rate of respiration as related to age. 

 J. Gen. Physiol, 10:33, 1926. 



