Seeds and Seedlings. 



25 



If seeds are planted in a pan of sawdust which is kept 

 revolving rapidly in a horizontal plane, centrifugal force 

 may be made to overcome gravity, so that the roots grow 

 away from the axis of rotation and the shoots toward it 

 (see Fig. 9). 



Fig. 7. 



Seedlings of Indian com grown in saw- 

 dust in a Petri dish while revolving 

 by clockworks one revolution per 

 hour. The axis of revolution is hori- 

 zontal, the plane of the dish vertical. 

 Gravity as a directive agent is elimi- 

 nated, and roots and shoots grow out 

 in the direction in which they happen 

 to be pointed. 



Fig. 8. 



Seedlings of Indian com grown in saw- 

 dust in a Petri dish which was kept 

 stationary in a vertical plane in the 

 position shown in the figure. Gravity 

 is acting as a directive agent, and the 

 roots find and take the downward and 

 the shoots the upward direction, irre- 

 spective of the directions toward which 

 they were originally pointing. 



Whatever part plants, as living beings, have taken in 

 the selection of gravity to direct their growth, a wonderful 

 discrimination has been exercised ; for, of the possibly 

 available forces of nature, gravity is the only one which 

 is practically constant in its strength, and in its direction 

 of action, through all times of day and seasons, and in 

 all positions over the earth's surface. The seedling can 

 therefore depend with certainty on its root and shoot 

 taking the right directions irrespective of the position in 



