FACTORS INFLUENCING TREE GROWTH. 17 
and will hardly live very long. In this stand also there appeared in 
the openings surrounded by the ditches a luxuriant herbaceous vege- 
tation strikingly different from that in the surrounding forest. 
In order to prove also that deficient soil moisture brought about 
by the competition of the roots was the sole cause of the death of 
pine reproduction under the shelter of mother trees, Fricke deter- 
mined the soil moisture in sample plots of which some were pene- 
trated by living roots, while in others the competition of the living 
roots was eliminated. In all these experiments the proportion of 
moisture in the soil was invariably greater in the plats free from 
living roots—usually two or three times greater, and occasionally 
four and even six times. 
The results of these experiments clearly show that the unsatis- 
factory condition of an undergrowth shaded laterally or from above 
is not due altogether to insufficient light, but to competition of the 
roots of the neighboring old trees; likewise that the presence and 
condition of shrubs, grasses, and mosses in the forest depends very 
little upon the amount of light, but are chiefly influenced by the 
degree of desiccation of the soil caused by the roots of the old trees. 
Thus the poor development of young growth directly under or near 
seed trees may be explained, not by shading alone, nor by the mechan- 
ical action of water dripping from the leaves and branches of the 
old trees, nor by excessive light reflected from the trunks, but by the 
moisture-sapping competition of the roots of the older trees. 
In these experiments, however, Fricke, by eliminating competition 
of the neighboring roots, created artificial conditions which do not 
exist in nature. Moreover, no photometric measurements of any 
kind were made during these experiments, and without such measure- 
ments the question of light requirements of species can not be settled. 
While the experiments bring out the importance of considering 
other factors besides hght in the hfe of the forest, they do not prove 
that the light requirements of all species is the same. 
On fresh soils, with an abundant supply of moisture, root competi- 
tion affects the growth of the seedlings only a little or not at all, and 
for this reason it is assumed that trees are more tolerant on fresh or 
moist soils than on dry soils. But even on the same kind of soil the 
effect of trees of different species upon the growth of seedlings is not 
the same. Trees with a strongly developed superficial-root system 
naturally desiccate the upper layers of the soil much more than trees 
with a compact, deep-root system. 
In filling fail places in plantations, the competition of the roots 
determines the success or failure of the operation. It happens only 
too often that the planting of fail places on dry or only moderately 
fresh soils meets with entire failure, because growth of the new 
