50 LIGHT IN RELATION TO TREE GROWTH. 
recognized as most light-demanding, namely, the pine and larch, 
absorb, in addition to the deep band in the red, only small portions of 
the blue and violet, while the shade-enduring spruce and beech absorb, 
besides the red, some orange and a large amount of blue, indigo, and 
violet. 
For measuring light intensities of the different rays of the solar 
spectrum he used a modified form of the Winger “light measurer,” 
manufactured by A. Kriiss,; Hamburg. The principle of the instru- 
ment is to measure the monochromatic lhght transmitted through a 
colored glass by comparing it with the standard lght of a benzine 
lamp passed through a glass of the same color. Two defects in the 
apparatus are pointed out. First, its capacity is not sufficient for 
all measurements; second, the glasses of the slide, with the exception 
of the red, are not of perfectly homogeneous color, with the result 
that the light which is transmitted through them is not absolutely 
monochromatic. The first of these difficulties is easily overcome by 
increasing the capacity of the instrument; the second, however, pre- 
sents a more serious obstacle, since perfectly monochromatic glasses, 
with the exception of red, are at present unobtainable. He presents 
the results of a number of measurements taken in stands of different 
composition. These results, with the exception of those for red 
light, are admitted to be inaccurate because of the defects in the 
apparatus; however, they are regarded by Zederbauer as sufficiently 
conclusive to demonstrate the correctness of the method. Measure- 
ments for the red rays only made by him at Purkersdorf, near 
Vienna, July 21, 1906, 9 a. m., sky clear, gave the following results: 
Amount of 
red light 
transmitted. 
Units. 
Picea excelsa (young) (Norway: Spruce)... 2. ..- 2... cssccecseeee ce une AOS aE ee eee a 10 
Hacusisylvatica (young) i (beech) sha ae ae eee see eee ee see ee eee ee ae ee eee | 10 
Garixeuropsca: (young): (arch)! Fae cece eis oe tase sree creel ene re Sie eee ein Seearenee eee 125 
Experiments at Mariabrunn, near Vienna, August 8, 1906, 6 p. m., 
sky rather cloudy, gave the following: 
Amount of red light 
transmitted. 
Piceaexcelsai(youns): (NorwaiyySpEuce) sees se eee a eeiee Geen see eee eee eee About 2 units. 
PIMUSISyLVeStris) Gyoune))(Scotchspine)-keseass cepa ee eeeeceeceeeeeeeeeeecereeeoeres About 12 units. 
[anixeeuropzea) (youn) (arch) * ase sao Seite Oe ee ee Ree eee anicoe naenieneeoearene About 11 units. 
Quercus robur pedunculata (young) (pedunculate oak)......-........--.---------- About 10 units 
TNH EO Pens ese ae esac ele oe se ere its See anaes eee iste cae Sree 220 units 
The results show a different absorption for each species, it being 
almost 10 times as great for the tolerant as for the intolerant species. 
