356 PLANT PHYSIOLOGY 



is attracting it with the force Y. Show by a diagram the direction of the 

 growth of the root and the magnitude of the resultant force acting upon it. 



4. How does the explanation of Child for the correlation phenomena differ 

 from that of Loeb? 



5. How can it be proved that geotropic response is not due to weight? 



6. Name a twiner of each class mentioned in the text. Give an example of a 

 species which twines in either direction and one which may reverse its direction. 



7. Is oxygen necessary for geotropic responses? 



REFERENCES 



Ball, N. G. — Rapid conduction of stimuli in Mimosa pudica. New Phyt., 



26:148, 1927. 

 Blackman and Paine. — Permeability of the pulvinus of Mimosa. Ann. Bot., 



32:69, 1918. 

 Bose, J. C. — The nervous impulse in plants. Scientia, 45:25, 1929. 

 Bose and Das. — Transmission of stimuli by plants. Nature, 115:49, 1925. 

 Child, C. — Certain aspects of the problem of physiological correlation. Am. 



J. Bot., 8:286, 1921. 

 Dixon, H. — Transmission of stimuli in plants. Nature, 114:626, 1924. 

 Guttenberg, H. — Why roots grow downward. Sci. Am. Mo., 3:311, 1921. 

 Hawker, L. E. — A quantitative study of the geotropism of seedlings with 



special reference to the nature and development of their statolith ap- 

 paratus. Ann. Bot., 46:121, 1932. 

 Keeble, F. — The plant commonwealth and its mode of government. Nature, 



114:55, 1924. 

 Lillie, R. — Nature of protoplasmic and nervous transmission. J. Phys. 



Chem., 24:165, 1920. 

 Loeb, J. — The quantitative basis of polarity in regeneration. J. Gen. Physiol., 



4:447, 1922. 

 Lund, E. J. — Internal distribution of the correlation potentials in the Douglas 



fir. Publ. Puget Sound Biol. Sta., 7:259, 1930. 

 Newcombe, F. — The supposed reversal of geotropic response. New Phyt., 



22:281, 1923. 

 Phillips, T. — Chemical and physical changes during geotropic response. 



Bot.Gaz., 69:168, 1920. 

 Prankard, T. L.— Statocytes of the wheat hulm. Bot. Gaz., 70:148, 1920. 

 Schley, E. — Geo-presentation and geo-reaction. Bot. Gaz., 70:69, 1920. 

 Small, J. — Changes of electrical conductivity and geotropism. Proc. Roy. 



Soc, 90B:349, 1918. 

 Snow, R. — Transmission of stimuli in plants. Nature, 115:82, 1925. 

 Stiles, W. — Irritability and movement in plants. Sci. Prog., 17:50, 1922; 



20:44, 1925; 22:40, 1927. 



