1914] CURRENT LITERATURE 249 
Climatic areas of the United States.—In a recent paper, LivINGsTON® has 
examined the various climatic data made available through the United States 
Weather Bureau, and finds that among the factors that may be related to plant 
growth, only precipitation and temperature have been measured with accuracy, 
and although the distribution of stations is far from ideal, the resulting data 
are satisfactory. The evaporation data of the Bureau are shown to be 
extremely meager, being limited to a single year. From the temperature 
tds Livincston has made a summation of the daily normal temperatures 
for the days within the frostless season, for a large series of stations, plotted 
these upon maps of the United States, and drawn isoclimatic lines. Upo 
these maps he has also drawn isoclimatic lines of (1) the average daily precipi- 
tation, (2) the average daily evaporation, and (3) the differences between the 
precipitation and evaporation for the same frostless period. e results are 
Tee maps in which are delimited areas upon the basis of temperature and upon 
the basis of a water relation. It is possible in this way to characterize climati- 
cally the area occupied by any plant or plant communit 
out the country for a period of 15 weeks, extending from May to September, 
of the prairie region and the eastern deciduous forest. This leads the author 
to conclude that this prairie region is a potential deciduous forest, a conclusion 
i accord with the success which has attended tree planting within much of 
this area and with the advance which the forest is at present making upon the 
Prairie, according to GLEASON and other workers. The mesophytism of the 
northwestern and northeastern conifer forest centers is demonstrated by aver- 
age weekly rates of evaporation of only about roo cc. The deciduous forest 
oo ies a region with a wee y summer rate of from 100 cc. to 200 cc., while a 
similar rate is shown for the southeastern conifer center, which might indicate 
that this formation is also potentially a deciduous forest. The semi-arid 
regions of the southwest show an average of from 300 cc. to 400 cc. weekly. 
‘ From these and other data it appears that the summer evaporation inten- 
ay furnishes a climatic criterion which is more promising for vegetational 
Studies than any other available meteorological data. It has the further 
advantage of being rather easily determined by the porous cup atmometer, and 
meh data would also be of great importance in agricultural as well as in ecologi- 
cal investigations —Gro, D. FuLrer. 
Darter 
« Livincston, B. E., Climatic areas of the United States as related to plant 
Stowth. Proc. Amer. Philos. Soc. 52: 257-275. 1913. y 
3 “Lt B. E., A study of the relation between summer evaporation inten- 
ln centers of plant distribution in the United States. Plant World 14: 205-222. 
