37 
 thinly-foliaged light-needing trees, such as the white oak or tulip tree, 
means killing it out, since it can not reproduce itself and thrive in the 
shade of its foregrown companions. 
It is evident that favorable soil conditions can be preserved only by 
a persistent close crown cover, such as the leafy species furnish. It is, 
however, not necessary that the crowns should all be on the same level, 
all of one story, so to speak; on the contrary, a denser cover can be 
secured if individual trees or groups of varying heights are placed 
together. Here, then, comes in the consideration of the relative rate of 
height growth. And it is an important one when we select a mixture 
or combination, for if we were to place together on an equal footing a 
light-needing with a shade-enduring kind, of which the latter is a more 
rapid grower, the former would soon be killed out. Now, as a rule, 
the light-needing species—but by no means all—are at first more rapid 
growers in height than the shade enduring ; but what they gain in ini- 
tial rapidity they lose in persistency; that is to say, they do not grow 
to as great a height as the leafy kinds, or at least after the first period 
of rapid growth they grow only slowly. 
Each species has its characteristic curve of height growth, charac- 
teristic especially in regard to the beginning of rapid ascent, to the 
position of the points at which the rates of growth change and to the 
point of culmination. This curve is, of course, modified for each spe- 
cies, accérding to the site upon which it grows. But as it is possible to 
construct a scale in which the various species can be ranged according 
to their relative capacity of shade endurance, so for given conditions 
and periods of growth they can be ranged in regard to their relative 
rate of height growth. In this way I have, for instance, ranged twelve 
kinds that are used in prairie planting according to their shade endur- 
ance and their rate of height growth during their youth: 
As to shade. As to rate of height growth. 
1. Box elder. 1. Cottonwood, 
2. Mulberry (?). 2. Soft maple. 
3. Elm. 3. Elm. 
4. Black cherry. 4. Locust. 
5. Osage orange. 5. Honey locust. , 
6. Catalpa. 6. Black cherry. 
7. Soft maple. 7. Catalpa. 
8. Locust. 8. Osage orange. 
9, Honey locust. 9. Box elder. 
10. Black walnut. 10. Black walnut. 
11. Ash. 11. Ash. 
12. Cottonwood, 12. Mulberry (?). 
This is not an immutable scale, but only a tentative proposition, and 
for the purpose of illustration in which the kinds placed widely apart 
will alone really retain their relative positions. We will find at the top 
of the first seale the most shade-enduring and at the head of the second 
