276 



BOTANICAL GAZETTE 



[OCTOBER 



such influences as thundershowers and sudden shifting of wind 

 to or from the lake with accompanying atmospheric changes in 

 temperature, relative humidity, etc. 



The usual pronounced saturation deficit that occurs on the 

 exposed sands is shown in fig. 10, which is a graph of readings 

 taken at station E on July 27. There was a very rapid rise to a 

 maximum at 9:30 a.m., at which time the water loss presumably 



Fig. 10.— Graph plotted for station E on July 27, showing typical saturation 

 deficit developed in open dune environments on clear days with temperature high 

 or relative humidity low. 



equaled the maximum translocating ability of the plant under the 

 conditions. Then as a deficiency was created in the cells by an 

 excessive loss, a drop in the index occurred until the turgor was 

 regained. A second low mode occurred at 4:00 p.m., a feature 

 recurring in all records taken at stations D and E, in which 

 an appreciable deficit was developed. Although the decline in 

 the relative transpiration index was considerable in the early 

 afternoon, there was no visible wilting. 



