28 BOTANICAL GAZETTE [JANUARY 
There is a difference that should be noted between the shade- 
producing capacity of the balsam and that of the birch. The 
former, with its many whorls of short branches close together and 
its opaque leaves, casts an exceedingly dense shadow which does 
not influence a large area. A moderately close stand of large 
balsams allows extremely little light to reach the ground. The 
birch (in its primeval forest form) influences a large area, but its 
shade is not dense, because of its comparatively thin crown and 
translucent leaves. Under the shade of large birches there is 
frequently a scattering of young growth, while under thrifty 
balsams there is rarely to be found any at all. Both conditions are 
well shown in the diagram of quadrat r. 
The effect of shading is seen also in the undergrowth. In the 
dense shadow of the balsams there is a mere sprinkling of herbs, 
and mosses are usually absent entirely, the ground being covered 
with a layer of tree waste. It is in shade of moderate density and 
in openings that the greatest luxuriance of mosses and herbs is 
found. The ground hemlock is excluded from most of the quadrat 
for the same reason, but in the lower right-hand corner there is an 
area completely occupied by a dense growth of it, which effectually 
prevents the establishment of any other species. 
QuApRAT 2 (fig. 7).—This quadrat shows the same features as 
the last. Group a contains a great number of young trees of similar 
age, mostly balsams, which have started as a consequence of one or 
more windfalls. Of the 40 balsams in the area, 33 are between the 
ages of 20 and 35 years, and within these limits, as shown by the 
diagram, there is a tendency for those of similar age to be neighbors. 
Numerous fallen trunks represent the former generation. The 
large balsam marked “12,” which was 121 years old—an unusual 
age for this species—was past maturity, and like the big spruce in 
the preceding quadrat was ineffective in producing shade. At 
b there is a part of an older group, 5 of the 7 balsams being between 
44 and 53 years old. The upper left-hand corner is dominated by 
a few old and large trees, balsams and birches, with practically no 
young ones—only a few beneath the birches. The shade in this 
area was dense and the undergrowth sparse, even the ground 
