THE WATER REACTION IN A LIVERWORT 265 



ity of the house was very low, and the temperature very high, 

 so that the exposed plants were subjected to conditions of extreme 

 aridity. Without doubt the glass house at the time was much 

 more arid than the habitat of the liverwort even in unusually dry 

 seasons. It was of interest, therefore, to watch the behavior of 

 the liverwort when its water fast was ended. Upon being given 

 water, it promptly unrolled, and assumed its active condition. 

 Although it was not determined, it is very evident, from such 

 responses of the plant, that it possesses a margin of safety by 

 which it can withstand conditions in nature almost inconceivably 

 arid. For this reason it seems doubtful whether aridity in itself 

 is the definitive factor limiting its lower distribution. 



THE PLANT WOBLl). VOL. 17. NO. 9, 1914 



