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PHARMACEUTICAL BOTANY 



to the earth's surface are diageotropic. The Lima Bean, Sarsa- 

 parilla, Poison Ivy, and other plants whose stems twine about sup- 

 ports exhibit lateral geotropism in their horizontal curvatures. 



Galvanotropism is the reaction of protoplasm to electrical stimuli. 

 In this connection it may be said that the degree of response bears 

 a definite relation to the intensity of the stimulus. No visible 

 external electrotropic reactions have been observed in higher plants, 



PIG. 31. Mimosa Spegazzini. Note the expanded condition of the leaves before 

 stimulation. (After Steckbeck.) 



although when their cells are examined microscopically, the reac- 

 tion becomes manifest. Kuhne has shown that when an. electric 

 current is passed through the hairs of the Spiderwort, the cytoplasm 

 becomes gathered into small globular masses. 



Thigmotropism is the response of living matter to mechanical 

 stimulation. Examples of this form of irritability appear to be far 

 less common among plants than among animals. Certain species 



