588 CARBOHYDRATE METABOLISM 



is apparently due to the maintenance of a relatively high concentration of 

 sugars in the cell sap, since under conditions unfavorable for rapid photo- 

 synthesis the accumulation of starch is greatly reduced. During the hours of 

 darkness, when a high sugar concentration of the cells is no longer maintained 

 by photosynthesis, the accumulated starch is rapidly reduced in amount by 

 transformation to sugars, in which form it is translocated out of the leaf. 



Discussion Questions 



1. Outline diagrammatlcally the stages in the synthesis of the principal polysac- 



charides from the hexose produced in photosynthesis. 



2. Why does sweet corn lose its sweetness soon after being picked? 



3. Wild cherry leaves are much more poisonous to cattle after they have been 



cut for a few days than when they are fresh. Explain. 



4. What will be the effect of girdling a stem on the time of appearance and 



intensity of red color in leaves of species in which anthocyanins are syn- 

 thesized? 



5. Heavy fertilization of red coleus plants greatly decreases the intensity of the 



red color of the leaves. Explain. 



6. Why are leaves of some species such as the black cherry usually yellow at 



the time of falling if they drop from the tree during a midsummer drought, 

 but generally red at the usual time of abscission in the autumn? 



7. Which of the common plant pigments are water soluble? which are fat soluble? 



Give reasons for your answers. 



Suggested for Collateral Reading 



Gortner, R. A. Outlines of biochemistry. 2nd Ed. John Wiley and Sons. 



New York. 1938. 

 Haas, P., and T. G. Hill. The chemistry of plmit products. 4th Ed. 



Longmans, Green and Co. London. 1928. 

 Harvey, R. B. Plant physiological chemistry. Century Co. New York. 



1930. 

 Haworth, W. N. The constitution of sugars. Longmans, Green and Co. 



London. 1929. 

 Kostychev, S. Chemical plant physiology. Translated by C. J. Lyon. P. 



Blakiston's Son and Co. Philadelphia. 1931. 

 Norman, A. G. Biochemistry of cellulose, polyuronides, lignin, etc. Ox- 

 ford Press. Oxford. 1937. 

 Onslow, M. W. The anthocyanin pigments of plants. 2nd Ed. Cambridge 



Univ. Press. Cambridge. 1925. 



Selected Bibliography 



Ahrns, W. Weitere Untersuchungen iiber die Abhdngigkeit des gegenseiti- 

 gen Mangenverhdltnisse der Kohlenhydrate im Laubblatt von IFasser- 

 gchalt. Bot. Archiv. 5: 234-259. 1924. 



