440) 
Rocky Mountains. ‘The general surface of the 
plains is similar to that of the prairies; and 
the character of the soil is also similar, except 
that it has not been so completely leached of 
its soluble salts, which are known by the popu- 
lar name of ‘alkali.’ There is, in fact, no 
line of demarkation between the prairies and 
plains except a climatic one, and there is no 
other reason for giving them each a different 
designation than that which has resulted from 
climatic causes; that is, westward from the 
Missouri River there is such a gradual dim- 
inution of the annual rainfall, that in western 
Kansas and Nebraska it is insufficient for the 
purposes of agriculture, while in the eastern 
part of those states respectively it is ample. 
In a general way, the line between the arid and 
humid regions may be said to pass northward 
medially through the two states just named, 
swerving somewhat to the westward as it passes 
through Dakota Territory to the British line. 
The trees which grew originally within the 
great prairie region were, with few exceptions, 
of the same kinds that grew in the wooded 
regions to the eastward of it; the more im- 
portant of the missing kinds being the beech, 
chestnut, tulip-tree, and the common locust- 
tree. The more common kinds of trees which 
grew there were oaks (four kinds), hickory 
(three kinds), maple (two kinds), elm, cotton- 
wood, black walnut, and linden. Among those 
which were less common were ash, honey-locust, 
sycamore, white walnut, mulberry, hackberry, 
Kentucky coffee-bean, and pecan. Besides 
these, a few pines and cedars grew upon the 
rocky cliffs of the valley-sides, and a few other 
trees were also scattered through the region ; 
but the conifers, as compared with angiosper- 
mous trees were rare and of little importance. 
I use here only the common names of the trees, 
as given in Gray’s ‘ Manual of botany.’ 
Traversing the prairie region from east to 
west and from south to north, it has been found 
that certain of the kinds of trees above named 
did not grow so far westward and northward, 
respectively, as others did. As regards the 
northern limitation of some, it was probably 
due mainly to temperature, and the western 
limitation of others was perhaps due, in part, 
to approaching aridity; but I think that to 
about the 98th meridian it was due to the only 
partially accomplished natural distribution of 
forest-trees from the eastward, which began at 
the close of the second glacial epoch. The first 
of the suggested causes of limitation has an 
important bearing upon the proper selection of 
trees for artificial planting in the northern por- 
tion of the prairie region. For example: while 
SCIENCE. 
[Von. IIL, No. 62. 
we may regard the oaks, maples, elm, cotton- 
wood, linden, and others as. practically without 
northern limit in the region under discussion, 
there are others, but fortunately they are mostly 
of less comparative value, which have their 
northern limit within this region. Among the 
latter may be mentioned the mulberry, honey- 
locust, Kentucky coffee-bean, and pecan. ‘The 
hickories and black walnut were plentiful in the 
immediate region of the Mississippi and east- 
ward, when the country was first known; and 
those trees seem to be the natural associates 
of the oaks. 
Now, there are two general physical condi- 
tions which are inimical to forest-growth ; and, 
wherever either of them is fully established, 
forests cannot exist. One of these conditions 
is an arctic climate, whether produced by high 
latitude or high elevation above the sea: and 
the other is an arid climate, or one where the 
annual rainfall is insufficient for the purposes 
of agriculture. I hold, that, in all regions of 
the earth which are not affected by either of 
these great climatic conditions, the foresting 
and reforesting of the surface, which is covered 
by a soil suitable for vegetable growth, is prac- 
ticable for certain kinds of trees. : 
Neither of these conditions exists within the 
great prairie region as I have indicated its 
boundaries. It should therefore be expected 
that forest-trees would grow there, even if no 
experimental proof of the fact had ever been 
made. As one goes westward from this region, 
however, he finds the country incapable of sup- 
porting a growth of forest-trees for the same 
reason that it will not support a farm-crop ; 
namely, because of its aridity.. Both trees 
and farm-crops can and do grow successfully 
upon the prairies, because they have sufficient 
moisture from rainfall. Also, if one should 
go northward far enough, he would, of course, 
come to a limit of the successful growth of trees, 
and also to a limit to the growth of any farm- 
crop; but that limit is far beyond the northern 
boundary of the region here discussed. 
The experiments of the dwellers upon the 
prairies have demonstrated that not only may 
all the indigenous trees of the adjacent valleys 
be made to grow on all varieties of its soil, 
but also that many kinds of eastern and exotic 
forest-trees, as well as most of the common 
fruit-trees, will grow there equally well. They 
have shown that the owner of any productive i 
farm in that great region need not be deterred 
from planting any of those trees upon it, from _ 
any other consideration than he would give to 
the planting of a farm-crop. 
- These experiments show that certain kinds 
