10 
increase greatly as one proceeds northward and westward from the 
eastern forest area. In the eastern border of the plains the planter 
has almost as great latitude in his choice of varieties as has the dweller 
within the forest, and he may select timbers cf the highest economic 
value, choosing several kinds, each adapted to specific uses, and plant- 
ing with them others whose only purpose is to promote the growth of 
his select trees. AS we go westward the possibilities of choice become 
more and more restricted, until in western Kansas and Nebraska, in 
the upper Missouri Valley and the high plains of Texas, New Mexico, 
and Colorado very few species can be relied upon, and these will have 
to be nurtured and cared for to a degree not dreamed of by the East- 
ern farmer. The exact limits of choice have yet to be determined. 
Thus far we must deal largely with generalities and inferences, which 
become more and more problematical as we proceed westward. 
The experimental plantings herein described in detail are given not 
only as a record of the beginnings of an important work, but as indi- 
cating what are believed to be useful mixtures of trees for planting in 
the West. Sufficient time has not elapsed, even in the oldest plantings 
described, for final conclusions to be drawn; but the notes on kinds will 
be found of interest in connection with the experiments, and the whole 
is believed to afford a basis for selection of trees for the various States 
included in the treeless area. 
While this bulletin has to do primarily with Western planting, it may 
be found a safe guide in many directions for forest planting within the 
timbered regions of the country, especially as to general principles 
involved. Experiments in planting in cut-over lands in the pineries of 
Minnesota and Pennsylvania have been begun by the Department, but 
are not yet sufficiently advanced to warrant even a progress report. 
CONDITIONS AFFECTING TREE GROWTH. 
In common with all plant life, trees require a certain amount of heat, 
light, and moisture for their development. These elements are so inter- 
dependent in their effect upon tree growth that it is almost impossible 
to consider one without keeping in mind the influence which the other 
two are constantly exerting. Thus, if we discuss the effect of heat upon 
tree growth, we are at once reminded that the action of heat and light 
are inseparable and that the result upon the same species in a moist 
and a dry region is quite different. It must be remembered that these 
elements are tiever dissociated in their influence on plant growth. 
Most trees have a wide range of endurance of heat, light, and mois- 
ture. The Red Cedar is a striking illustration of adaptability to a great 
range of conditions. It is found in the swamps of southern Florida, 
furnishing wood for pencils; on the dry, exposed foothills of the Rocky 
Mountains, where it is reduced to a mere shrub; along the Platte 
tiver Valley in Nebraska, in the northern forests of Maine, and reaches 
its best development in the limestone soils of eastern Tennessee—an 
