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 hcud doiviiward hy the more rapid growth of its 

 upper as compared u'ith its u)ider 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 Ti-oody 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. Eoots with an unequal 



