METHODS OF DETERMINING TOLERANCE. 29 
even an entire lack of annual rings at breastheight, and in such cases 
the relative height of the tree can not be a true indication of its 
tolerance. 
ARTIFICIAL SHADING. 
With empirical methods must also be classed the experiments in 
artificial shading, to determine the relative tolerance of forest trees. 
The first experiment of this kind was made in 1866 by Kraft (1878, 
v. 54: 164-167), who planted under the cover of a 50-year-old oak 
forest (of artificial origin) seedlings of other forest trees, and eight 
years later, in 1874, measured the heights and diameters of the 
planted seedlings. On the basis of the results of these experiments 
and observations on the forest in general, Kraft arranged the species, 
beginning with the most tolerant, in the following order: 
Fagus and Abies (beech and fir). Betula (birch). 
Carpinus (hornbeam). Pinus strobus (white pine). 
Acer (maple). Larix (larch). 
Picea (spruce). Pinus austriaca (Austrian pine). 
Fraxvinus (ash). Pinus sylwestris (Scotch pine). 
Another experiment of this kind was made in Russia by Nikolsky 
(1881) on three rows of pine (intolerant) and spruce (tolerant) for 
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PINUS | FINUS _-LARIX FAGUS — TILIA. CARPINUS FRAXINUS. ULMUS 
a AUSTRIACA SILVESTRIS EUROPEA BETULUS : LFFUSA 
CON/FERS. HARDWOODS 
(a) AVERAGE HEIGHT OF STEMS OF SEEDLINGS ABOVE GROUND 
WITH BIFFERENT CONDITIONS OF SHADE 
WAG OANGLOS 
‘NCHES 
OND 
PINUS. PINUS. LARIX 
AUSTRIACA SILVESTALS EUROFEA 
na CON/ FERS 
(6) AVERAGE DIAMETER OF SEEDLINGS AT GROUND 
WITH DIFFERENT CONO/TIONS OF SHADE 
Fig. 3.—Results of experiments with shading seedlings. 
the purpose of determining the influence which shade has upon the 
growth of 1-year-old spruce and pine. In this experiment the great- 
est length of stem (from the cotyledons to the terminal buds) was 
found in trees which grew in the shaded row; the length of the entire 
plant above ground increased with increase in shade; the length of 
the main root, as well as the number and the total length of the lat- 
eral roots, however, diminished with increase in shade, while the 
