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sin, has published in Bulletin No. 42 of the Wisconsin Agricultural 
Experiment Station interesting data showing the effect of wind in 
increasing evaporation, and also the great utility of groves of trees 
as wind-breaks and crop protectors. Doubtless the ameliorating effects 
of wind-breaks would be much greater in the plains than in Wisconsin, 
all meteorological conditions there being more severe. 
Series of observations on atmospheric humidity at the several experi- 
ment stations show that the relative humidity seldom falls below 50 
for more than a day or two ata time, and that such days of extreme 
aridity of the atmosphere are often followed immediately by periods 
when the air is of relatively high humidity, permitting a recovery on 
the part of vegetation from the ill effects of the excessive evaporation 
which must have occurred during the very dry days. It has been 
demonstrated that the amount of evaporation from plants is directly 
dependent upon the available water supply, other things being equal. 
Of course, a low degree of humidity in the air will tend to increase 
evaporation, and trees can not be expected to make the vigorous 
growth under such conditions that is possible in moister regions. 
The constant winds are a principal factor in the aridity of the plains. 
With no obstruction for hundreds of miles, they blow over an area 
devoid of forests and of large bodies of water. [ven in a region of 
abundant rainfall, such continuous air movement would cause greatly 
increased evaporation and have a bad effect on plant growth, but with 
a limited precipitation every means of protection should be employed. 
It is not to be supposed that trees will grow to the size in the wind- 
swept plains that the same species will attain within the forest area. 
The heavy winds of the plains suggest the planting of forest trees in 
masses or large groves, rather than in long narrow strips, as was the 
general practice under the timber-culture law. If ten acres be set aside 
for a grove, the trees will not only form a better windbreak if planted 
in a square or a rectangle of but little greater length than breadth, but 
in their more compact form they will hold the snows better and will 
themselves suffer much less from the action of the winds. The outer 
rows of trees will afford protection for the greater part of the plantation. 
This form of grove is especially useful if it be protected by planting, 
on all sides and a few rods from its borders, a hedge row of trees that 
shall serve as a wind mantle. In the North such a hedge will cause 
the formation of drifts between the hedge and the grove instead of 
within the grove itself, and the damage by breaking when the snow 
melts will thus be obviated. Moreover, the water from such melting 
drifts is largely absorbed by the soil, and thus saved to the farm. 
SELECTION OF SPECIES. 
In the selection of species for Western planting, it is not always 
possible for the grower to be governed exclusively by considerations 
of adaptability to his conditions and utility of the timber. Oftentimes 
