148 
Journal of Agricultural Research 
Vol. XXIV. No. a 
The important thing shown by Table XIX is that the wilting co¬ 
efficients of yellow pine, Douglas fir, and Engelmann spruce are essentially 
the same in all the soils, while that for lodgepole pine is much higher. 
There is, moreover, no evident reason for the fact that in some of the 
soils (sandstone and prairie shale) the wilting coefficient for spruce is 
lower than for either pine or Douglas fir. We must, at least at this stage, 
regard these variations as accidental.^ 
It will now be well worth while to determine whether, as between any 
two of these apparently equal species, a greater number of results brings 
out any difference. A very considerable amount of data has been secured 
on Douglas fir and spruce growing in the same soils. In introducing 
these data it is desirable to point out: 
I. That ocular observations on wilting, especially when the moisture 
supply is steadily declining, tend to favor Douglas fir, because that 
species has a much stronger and more fibrous stem and rarely collapses. 
The evidence of wilting is, therefore, much less plain than in the frail 
spruce seedling, and, it seems likely, may not be obtained until a day or 
two after the fatal condition has first existed. 
Table ^Wilting coefficients of the four important species in 5 types of soil 
i ■ . 
Capillary 
moisture. 
Moisture 
Mean wilting coefficients, best 25 per cent of the 
seedlings. 
kind of soil. 
equivalent 
100 grav¬ 
ity. 
Yellow 
pine. 
Lodgepole 
pine. 
Douglas 
fir. 
Engel¬ 
mann 
spruce. 
Average 
of four. 
Gtaniticf gfavel sandy 
Per cent. 
Per cent. 
Per cent. 
Per cent. 
Per cent. 
Per cent. 
Per cent. 
loain.____ 
26.58 
lO* 55 
2. 28 
2. 42 
2. 16 
2. 26 
2. 28 
Composite limestone 
loam.... 
31- 85 
22. 00 
3 * 23 
4. 12 
3 - 56 
3 - 50 
3. 60 
Coniposite sandstone 
loam.... 
35-34 
21. 77 
4. 10 
5 - 29 
4*30 
3-93 
4.40 
Prairie silt loam from 
shale... 
37 - 77 
28. 79 
7. 80 
8.69 
7 - 79 
7-43 
7 * 93 
Composite lava silt 
loam ....... 
43 - 16 
27. 80 
4 - 52 
6. 00 
4 * 97 
4.87 
5-09 
Average. 
4. 39 
5-30 
4.56 
4.40 1 
1 4.66 
2. That in the early stages of development Douglas fir roots more 
strongly than spruce and its roots reach a greater soil area, but 
particularly in these pan tests they reach the deepest layer of soil 
which may not be drawn on at all by the spruce if the wilting is accom¬ 
plished at an early age. (See Plate 7, B.) 
3. TherJefore, in these tests it is evident that if spruce seedlings tolerate 
as great a degree of drought as fir, the moisture being known only through 
the whole pan weight, it must be through greater aHlity to extract water 
from the soil. 
From Table XX it will be evident that the wilting coefficient for spruce 
is, on the whole, higher than that for Douglas fir. The difference is only 
ateiit 3 p^ cent of the value for fir. Of the 23 cases cited, only 6 give 
spruce a lower value than fir, and 5 of these 6 are among the loose gravels 
..j. '....I-—;—.—^---------^^---— 
’ Since the foregoing statement was written very convincing results have become available.showing the 
different effects of each of these soils in stimulating the ^wth of each species, both according to chemical 
composition of the soil and the concentration of its solution. It can hardly be questioned that this has a 
d ir ect bearing on t&e behavior of the seedlings as Uie wilting point is approach^, and in fact that this entire 
problem is' quite as much one chendcai rdationS ascf the physical relations which have been discussed in 
this paper. It is hoped that something may be published on this chemical phase in the nbir future. 
