METHODS OF DETERMINING TOLERANCE. 51 
Measurements for all the colors of the spectrum at Krems, April 22, 
1907, 10 a. m., sky partly cloudy, gave the following results: 
Units of transmitted light. 
Red. | Orange.| Yellow.| Green. | Blue. | Indigo. | Violet. 
| ff | f 
Picea canadensis (white spruce)....-.... 75 100 200 250 300 500+ 100 
Pinus sylvestris (Scotch pine).........-. 225 320 500 500-++ 450 500+ 300 
Measurements at Mariabrunn, June 14, 1907, 3-4 p. m., sky cloudy, 
gave the following results: 
Units of transmitted light. 
Red. | Orange.) Yellow.| Green. | Blue. | Indigo. | Violet. 
Picea excelsa (Norway spruce)........-- 2 7 12 100 40 200 100 
Pinus sylvestris (Scotch pine).......... 150 200 470 500+ 500+ 500+ 200 
Larix europea (Huropean larch)........ 50 80 90 250 200 500+ 100 
Quercus rebur pedunculata (peduncu- 
LAGER O GAKS) rere anne spy space oe ma Rr ple 24 50 100 100 150 250 50 
These measurements show a different absorption for each species, 
not only in the red but also in the other colors of the spectrum. 
According to Zederbauer, the results of his investigations, includ- 
ing measurements not given here, show that the intolerant species, 
pine, larch, and birch, absorb very little in the indigo, and less than 
the tolerant species in the red, blue, and violet. It will thus be seen 
that a tolerant species such as spruce growing beneath an intolerant 
species such as pine is capable of utilizing a great deal of the light 
which is let through by the latter. The light beneath the overshaded 
spruce will be found to have undergone a second sifting, as it were, 
thus producing a spectrum deficient in red, blue, and violet. 
WIESNER’S INVESTIGATIONS. 
Zederbauer’s criticism of the photochemical method of measuring 
light in the forest probably holds good for dense forests, such as 
those of spruce or hemlock in this country, in which the light is 
mostly transmitted or reflected ght and therefore of a different 
composition from light in the open. In open forests, such as the 
jongleaf pine and western yellow pine forests of the South and South- 
west, in which most of the light is of the same composition as that 
in the open except that it is of lower intensity, the photochemical 
method undoubtedly gives correct values. Wiesner, while not denying 
the possible change in the composition of the light after it passes 
through the crowns of the trees, maintains that the light even in 
dense forests is practically of the same composition as that in the 
