AN INVESTIGATION OF THE CAUSES OF 



AUTONOMIC MOVEMENTS IN 



SUCCULENT PLANTS 



EDITH BELLAMY SHREVE 



Tucson, Arizona 



I. 



The stucty of autonomic movements in plants has attracted 

 the attention of many notable workers throughout several 

 decades, but as yet very few have been able to attain an ap- 

 proach to the goal of ultimate causation. Various kinds of move- 

 ments have received attention and their causes have been ascribed 

 to such things as changes in geotropic irritability, differential 

 growth, changes in the turgidity of special organs, caused in 

 turn by changes in permeability of protoplasm, to temperature, 

 to light, etc. ; but the causes of the changes in geotropic irritability 

 (whatever the term may mean), of differential growth, of per- 

 meability changes, or the mechanism by which light and tem- 

 perature act, have not been found. There have come to the 

 attention of the writer no papers dealing with autonomic move- 

 ments in succulents and it seemed probable that a study of move- 

 ments in this class of plants might bring to light new facts which 

 would in the end aid in the discovery of the ultimate physico- 

 chemical causes for at least one class of movements. 



In the following report new facts regarding movements do 

 appear and their causes are traced to a physical source but this 

 source is, alas, still far from the ultimate cause. This paper 

 will, however, be followed at an early date by another which 

 will contain the results of a further research into the mechanism 

 of the physical source mentioned above. In the present paper 

 the usual terms "irritability," "internal stimulus," "response" 

 have been avoided because in the opinion of the writer they mere- 



297 



THE PLANT WORLD, VOL. 18, NO. 11, 1915 



