ROOTS *59 
noticed that the growing tips of the roots of the sprouting 
peas point almost directly outward from the center of the 
disk on which the seedlings are fastened. Explain the differ- 
ence between this result and that obtained in Exp. XX. 
- EXPERIMENT XX 
How do Primary Roots point when uninfluenced by Gravity? Pin 
some soaked Windsor beans to a large flat cork, cover them with 
thoroughly moistened chopped peat-moss, and cover this with a thin 
glass crystallizing dish. Set the cork on edge. Prepare another 
cork in the same way, attach it to a clinostat, and keep it slowly 
revolving in a vertical position for from three to five days. Com- 
pare the directions taken by the roots on the stationary and on the 
revolving cork. 
’ 71. Direction taken by Secondary Roots. — As the stu- 
dent has already noticed in the seedlings which he has 
studied, the branches of the primary root usually make a 
considerable angle with it (Fig. 2). 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 horizon- 
tal or nearly horizontal position of large secondary roots 
is the most advantageous arrangement to make them use- 
ful in staying or guying the stem above, to prevent it from 
being blown over by the wind. 
72. 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. 
1 See Ganong’s Teaching Botanist, pp. 182-186, for complete directions. 
The brief statement above given is abstracted from that of Professor Ganong. 
