38 
scale the most rapid growers among those named. If we can make, 
therefore, a combination of these, we will succeed in obtaining the two 
points to be gained, the densest crown cover in varying tiers, and the 
light-needing kinds overgrowing the shade-enduring, which allows the 
largest number of individuals on the area. 
I must once more caution you against accepting the above scale as 
definitely correct. Many conditions of soil and climate modify the 
behavior of trees. For instance, the black walnut has a tolerably dense 
foliage when quite young, but except on rich bottom lands it thins out 
very soon, and, since it leaves out late in the season and loses its foliage 
early in the fall, it must be considered as one of those which do not fur- 
nish desirable shade conditions. In regard to its height growth, too, 
it may vary; but, as far as my observations go, while it shoots up 
rapidly at first in the prairie, it almost stops growing when 12 or 15 
years old. On the whole we must study the behavior of our trees still 
further before we can speak with assurance as to the best selection and 
combination. But we can formulate the principles upon which proper 
selection and combination rests, and having then concluded never to 
plant one kind by itself—which is the unfortunate practice in most 
prairie planting—nor to plant several species in combination without 
knowing why they should be combined, we can lay down the following 
rules for making the selection: : 
HOW TO MIX, 
_ Rule 1.—The main growth, i. ¢., the one that occupies the larger part 
of the ground, must be of a kind that improves soil conditions, namely, 
a densely foliaged, shade-enduring kind, which does not lose its shad- 
ing capacity with age. 
Rule 2.—Densely foliaged kinds may be grouped together, if the slow 
grower will endure the shade of the rapid grower, or can be protected 
against its supremacy by being planted in larger specimens, or in ad- 
vance of the former, or in larger numbers, or if its gradual killing out 
after it has served its function of soil cover is not objected to. 
Rule 3.—Thinly foliaged kinds should never be grouped together 
where soil humidity is to be preserved, unless no leafy tree can be 
found to fit the locality. 
Rule 4.—In grouping light needing with shade-enduring kinds, the 
former must be more rapid growers or must otherwise be given an ad- 
vantage. 
Rule 5.—The mixing in of the thinly foliaged trees is preferably done 
singly and not in groups, unless special soil conditions necessitate the 
latter method. 
With such rules and considerations in mind, the proper practice in 
prairie planting is indicated. . 
The first and main object to be attained there is to create a soil cover. 
In Russia, under very similar conditions to those of our prairies, it has 
