1914] GATES—XEROPHILY 485 
during a very cold winter day, it is obvious how great is the advan- 
tage of this ability to lessen the demands upon the root and con- 
ducting systems at a time when the ground is frozen solid. 
6. The transpiration per unit surface of the evergreen shrubs 
was very decidedly greater (4-10-30 and more times) than that 
of the deciduous shrubs during the winter under both outdoor 
conditions and indoor conditions which simulated warm spells in 
winter. 
7. Among the evergreen ericads the relative rates of tran- 
spiration varied in the inverse order of their exposure and of their 
xerophytic structure. Chamaedaphne, which is the most exposed 
and the most xerophytic, has the lowest rates of transpiration and 
conduction. 
8. During an average southern Michigan winter, protection by 
snow is not essential to the preservation of Chamaedaphne. In an 
extremely severe winter (1911-1912) absence of snow protection 
results in the killing of parts not so protected. 
9. During the coldest weather (—29°) it did not appear that 
twigs or leaves of Chamaedaphne were frozen, as they were either 
perfectly pliable to handling or cracked as dry leaves. 
10. Experimentation upon the rate of conduction by the lithium 
nitrate method showed a relatively higher rate at first, following 
the shock of cutting. Variations in external factors could not be 
arranged for a given plant because the shortness of the stem necessi- 
tated a short time of experimentation, and in order to obtain the 
data the stem had to be destroyed. 
11. The rate of conduction was faster from warmer solutions, 
but was never zero when the solution was frozen. As the tran- 
spiration varied similarly, it seems obvious that the transpiration 
exercises a general regulatory function on the rate of conduction, 
similar to that which it exercises upon water absorption. The 
regulation is not exact, for in incipiently dry plants the rate of 
absorption and conduction is relatively greater than the rate of 
transpiration, while in turgid plants transpiration may be greater 
than absorption or conduction. 
12. While the rate of conduction was relatively higher in the 
evergreen ericads than in other shrubs during the winter, leafless 
