130 BOTANICAL GAZETTE [AUGUST 
not take up so much water as does hot air; consequently the addi- } 
tional amount of water which the atmosphere is capable of taking 
-up to become saturated, that is, the evaporating power of the air, 
is greater here than at Marquette. The amount of evaporation 
also depends upon several other factors and conditions; the values 
of these will be taken into consideration below. Where evapora- 
tion is nearly as great as precipitation, the seasonal distribution 
of rainfall and humidity is a matter of greatest importance, for 
it is known that scanty rainfall throughout the year, or relative 
dryness of air and soil during the growing season, favors the devel- 
opment of xerophytic forms in almost any region. The relative 
humidity of Columbus and vicinity is only slightly less when 
compared with the north, the percentage of saturation ranging 
from 79 to 80 respectively. The distribution varies during the 
year only to a small extent between the month of least and that 
of greatest normal humidity. 
The rate of movement of air currents is, no doubt, of great 
importance to vegetation, not only because of the direct mechani- 
‘cal effect and the indirect physiological action in increasing the 
evaporating power of the air, but also because transpiration 
increases with the velocity of the wind. That wind is an eco- 
logical factor of the greatest importance has been emphasized 
by many authors. KratmaAn and Warminc regard xerophytic 
structures in plants as acquired and necessary, on account of strong 
drying winds in exposed places. Even humid atmosphere when 
continually renewed leads to strong transpiration, and the danger 
may be decreased only as protection is provided either through 
density and height of species, or admixture of a variety of species 
in a community of plants. The average maximum velocity of 
wind does not vary greatly between Columbus and Marquette, 
and hence the influence of wind, though considerable in more 
exposed places, has apparently little relation to the differences 
to be accounted for in the character of the local vegetation. 
Briefly summarized, the region about Columbus and Buckeye 
Lake is characterized by a longer growing period with a relatively 
higher sum total of temperature exposure, a milder winter with 
normally slight variations, well distributed rainfall, and a relatively 
