406 
The Ohio Naturalist. 
[Vol. Ill, No. 6. 
root action is practically nothing, then evaporation into an air of 
low relative humidity may take place to such an extent as to 
prove injurious. No water is taken by the roots from the soil to 
take the place of that evaporated. During the growing season 
the effect of a low relative humidity, as in case of hot, dry winds, 
is too well known to need further comment. 
The relative humidity of the Northern and Western United 
States is from five to ten per cent, higher in winter than in sum- 
mer, but in the Gulf States and lower Atlantic States conditions 
are fairly constant the year through. The highest relative humid- 
ity is to be found along the northern Pacific coast and to the 
east and southeast of Lake Superior. The westerly air currents 
rising from the Pacific to the crest of the mountains are consid- 
erably cooled and saturation is produced to such an extent that 
much of the moisture is precipitated and never gets over the 
mountains. In this manner a high relative humidity is brought 
about along the coast. 
In the case of the Great Lakes we have another factor in opera- 
tion. The westerly air currents in drifting across the waters 
are often considerably cooled and also take up more or less 
moisture, so that a region of high relative humidity must result 
east of the lakes. 
Ohio presents some rather peculiar conditions with respect to 
humidity. As may be seen in the plate, the January map shows 
a streak coming down from the northwest and traversing the 
State diagonally in which the relative humidity is above eighty 
per cent. The air in that streak is jnst as "moist” as the air of 
Florida. From Map II of the January article referred to it may 
be seen that this streak includes that part of the State having the 
least total annual precipitation, and only a small part of those 
sections of the State having the greatest annual precipitation. 
The total annual precipitation and the relative humidity appear 
to have no connection whatever. 
Turning again to the January article, Map VII shows that 
during winter the least average minimum temperatures occur in 
the northwestern and central portions of the State, and are central 
in the region of high relative humidity. The inference to be 
drawn is that the higher relative humidity results from the lower 
temperature. It is not readily apparent, however, why this region 
should have its longer direction at right angles to the prevailingly 
southwestern direction of the winds, but perhaps this may be due 
in some measure to the difference in temperature of winds from 
different directions. The general direction of storms in our region 
is from west to east. Around the areas of low barometric pressure, 
usually the warm stormy areas, the winds revolve in a counter- 
clockwise direction, while around areas of high barometric pres- 
sure, those of clear cold weather, the revolution of the wind is in 
