30 LIGHT IN RELATION TO TREE GROWTH. 
total length of all roots in rows with great light intensity was greater 
than the total length of all the roots in the shaded rows; in pine 
seven and a half times and in spruce two times; at the same time the 
weight of the dry substance of seedlings which grew in full light 
was greater (in pine five times, in spruce three times) than that of 
seedlings which grew in heavy shade. 
The Swiss experiment station* made, in 1893 and 1897 (Badoux, 
1898, v. 6: 29-86), experiments on 11 tree species (5 rows of each) 
with different degrees of shading; rows entirely unshaded, one-fourth, 
one-half, and two-thirds shaded. In these experiments the least sen- 
sitive to shading proved 
to be spruce and fir, 
which had almost the 
same average height 
growth at different de- 
grees of shading. With 
pines, larch, beech, and 
ash the growth in height, 
on the contrary, de- 
creased 1n proportion to 
shading. Finally, with 
basswood, blue beech, 
and elm, the growth in 
diameter decreased in 
proportion to shading, 
while the growth in 
height was but little af- 
fected. The results of 
these experiments are 
Fic. 4.—Cross section of a beach leaf. a, Grown in presented in fig. 3, where 
the shade; 0, grown in full light. for each species 1s given 
the average height of the stem above the ground in inches, and for fir, 
spruce, Austrian pine, Scotch pine, and larch also the average diam- 
eter of the stem above ground. 
ANATOMICAL AND PHYSIOLOGICAL METHODS. 
The cause of the difference in the ability of plants to endure shade 
must, as already stated, be sought in the leaves, chiefly in their ana- 
tomical structure and in the character of the chlorophyll. 
STRUCTURE OF LEAVES. 
Stahl’s (1880 and 1883) experiments have conclusively shown that 
light exerts a very powerful influence upon the external and internal 
structure of the leaves. Shade-enduring plants (for instance, Owalis 
1These experiments seem to show that the development of seedlings of an intolerant 
species is affected more by variation in light intensity than is that of a tolerant species, 
and therefore that their behavior in different light intensities may serve as a criterion to 
determine their tolerance. 
