1914] GATES—X EROPHILY 455 
thorough drying and therefore death result. This same process 
has already been shown by KiHitMAN (24) to be the cause of the 
arctic tree line. 
That the water supply for ericads in Michigan peat bogs is 
actually ample to their needs is clearly demonstrated by experi- 
mentation upon potted plants, for even under the very extreme 
evaporating power of the air on July 5, 1912, the maximum rate of 
transpiration was contemporaneous with the maximum evapo- 
rating power of the air. Conditions of atmospheric evaporating 
power in Michigan are never as high as those of Arizona, where 
Lioyp (32) found that the fall in the rate of transpiration in oco- 
tillo (Fouquieria splendens) occurred before that of the maximum 
evaporating power of the air. Whether these results may be the 
true expression of the behavior of rooted plants may be open to 
question, as Lioyp used cuttings to experiment with. It was 
found in the present investigation that on days of extreme evapo- 
rating power in Michigan a decline in the transpiration rate in 
advance of the time of maximum evaporating power of the air did 
actually occur in cuttings, but was not exhibited in potted plants 
of the same species. Such a check in transpiration is occasioned 
by what Livincston and Brown (28) have termed ‘incipient 
drying,” in the course of which the evaporating menisci have 
retreated into the pores of the cells, thereby not only decreasing 
the amount of the exposed surfaces, but also greatly increasing 
the surface tension of these evaporating surfaces, which decreases the 
vapor tension and consequently the rate of vaporization (RENNER 
39, 40, and PatreNn 38). The increase in the concentration of cell 
sap which accompanies this check in water removal further retards 
vaporization. A very serviceable pictorial presentation of the 
matter is given by MacDoucat (34). 
The recent work of some investigators seems to withdraw the 
foundations from the theory of the efficient function of the stomates 
as the regulators of transpiration (LLoyvD 32, 33, and others). 
That closed stomates are efficient means of lowering transpiration 
has been demonstrated by many authors (BURGERSTEIN 3, and 
Deir 15). The closure of the stomates of evergreen plants during 
winter, which has been demonstrated by several investigators, 
