41 
This much, however, may be maintained, that seeds procured from 
driest and coolest localitigs in the range of the species promise seed- 
lings of greater hardiness than those from the more humid and warmer 
climates. 
We need in our treeless regions several arboreta for trials, carefully 
conducted, of adaptation of new kinds. . 
The list of trees which have been tried and found capable of more or 
less extended use is already quite considerable and includes the fol- 
lowing: Of conifers, white cedar, white, red, Scotch, Austrian, and bull 
pine, Douglas spruce, and farther south red cedar and bald cypress. 
Of deviduous trees the hardiest seem to be white and green ash, white 
elm, white and yellow birch, box elder, soft maple, basswood, besides 
the cottonwoods, Lombardy poplar, and white willow; and as we go 
southward the choice increases with black locust, catalpa, mulberry, 
black cherry, walnut, some oaks, chestnut, with the further addition of 
honey locust, Osage orange, pecan, and lastly acacias and eucalyptus 
in the extreme southwestern latitudes. 
As regards adaptability to soil, we need consider only the physical 
conditions of the soil, for forest trees require such small amounts ot 
mineral matter that it is questionable whether a soil could be found that 
does not contain in sufficiency those that seem necessary. 
Of physical conditions, it is especially the depth, the grain, and mois- 
ture that determines adaptability of kinds. While we may say that 
all trees will grow best on any soil which is deep (that is, where no im- 
penetrable layer of rock or hardpan or soil water is to be found within, 
say, 3 to 6 feet of the surface), of medium grain (not so compact that 
water and roots can not easily penetrate, nor so loose or coarse-grained 
that it can not hold water), and with an even, continuous supply of 
water, there are some trees which can thrive under less favorable con- 
ditions. | 
This adaptation is probably due to the development of the root sys- 
tem of these trees, but at the same time no doubt to the amount of 
water required by the foliage to satisfy transpiration. 
For planting in the dry regions no doubt those kinds recommend 
themselves which develop naturally a vigorous root system into the 
depth, because this enables them to utilize the percolating moisture 
through alonger space of time and over a larger area. The black lo- 
cust and catalpa, black cherry, the oaks and maples, and the pines, with 
a number of other conifers, have such root systems as to insure success 
where more shallow-rooted kinds would fail. 
It would lengthen this paper beyond the bounds of the present inten- 
tion were I to attempt to discuss in detail the merits and demerits of 
those species which have proved themselves so far adapted to use in 
these regions, and still further of the many which still await trial. Suf- 
fice it to admit that this chapter needs still much more material, derived 
from experiment and experience, before we can finish i. 
