CHAPTER V 



WE shall consider this subject under three heads: (I) Methods 

 of Study ; (II) Effect of Gravity upon the Structure of Proto- 

 plasm ; (III) Control of Locomotion by Gravity--Geotaxis. 



1. METHODS OF STUDY 



Under normal circumstances gravity acts upon organisms 

 continuously, uniformly, and in one direction only at a time. 

 In this respect it is widely different from most of the agents 



FIG. 21. Diagram of the essential part of a klinostat. A rotating block or drum, 

 to which tubes containing the geotactic organisms may be attached in the position 

 indicated. 



which we have to consider. Since its action is uniform it can 

 be varied only in an indirect way ; i.e. by turning the organism 

 or by replacing gravity in part by a force working in another 

 direction. One of the simplest ways of turning the organism 

 so as to eliminate gravity is by means of the klinostat (Fig. 21). 

 This is made in various forms, and consists essentially of a 

 horizontal rod supported near the ends and made to revolve 

 about its long axis by clockwork. Towards the middle of the 

 rod, or at one end, is rigidly affixed a block to which may be 



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