ROOTS 41 
generally think of it as a thing that needs discussion or 
explanation. Since they are pretty flexible, it may seem 
as though young and slender roots merely hung down 
by their own weight, like so many bits of wet cotton 
twine. But a very little experimenting will answer the 
question whether this is really the case. Making fine 
equidistant cross-marks with ink along the upper and the 
lower surface of a root that is about to bend downward at 
the tip readily shows that those of the upper series soon 
come to be farther apart, — in other words, that the root is 
forced to bend downward by the more rapid growth of its 
upper as compared with its under surface. 
53. Direction taken by Secondary Roots. — As the student 
has already noticed in the seedlings which he has studied, 
the branches of the primary root usually make a consider- 
able angle with it. Often they run out for long distances 
almost horizontally. This is especially common in the roots 
of forest trees, above all in cone-bearing trees, such as pines 
and hemlocks. This horizontal or nearly horizontal position 
of large secondary roots is the most advantageous arrange- 
ment to make them useful in staying or guying the stem 
above to prevent it from being blown over by the wind. 
54. Fitness of the Root for its Position and Work. — The 
distribution of material in the woody roots of trees and 
shrubs and their behavior in the soil show many adapta-. 
tions to the conditions by which the roots are surrounded. 
The growing tip of the root, as it pushes its way through 
the soil, is exposed to bruises; but these are largely warded 
off by the root-cap. The tip also shows a remarkable 
sensitiveness to contact with hard objects, so that when 
touched by one it swerves aside and thus finds its way 
downward by the easiest path. Roots with an unequal 
