190 PLANT PHYSIOLOGY 



l^lied to them, whether this be ui^ward or downward. This 

 phenomenon is called rheotaxit:,*' but it is not certain that 

 it is not a resjionse to obscure chemical stimuli rather 

 than to a current of water merely'. Rheotaxis and rheo- 

 tropism are therefore probably distinct phenomena. The 

 signiflcance of rheotropism is not understood. 



T'igure 13. I'osti'kiu Falni:rfornii.s. Sea-palni8 at Point Lobos. near 

 Monterey, California. Height about 2 feet, riiotograph by Dr. W. A. 

 Shaw. 



Waves and tides liave not been studied experimentally in 

 their mechanical relation to plants. It may be inferred, 

 perhaps, that they produce movements which stimu- 

 late the plants exposed. Certainly plants which are to 

 withstand the poundino' of tlie waves must grow propor- 

 tionally resistant. Is this simply a case of the survival 

 of the accidentally toughest iind fittest, or do tide and surf 

 plants irritably react to the rude stimuli to which they are 



* Stahl. E. Zur Biologie der Myxoniyceten. Bot. Zeitung. 1884. 



