GEOTROPISM. 119 



EXPERIMENT 45. This may be tested for steins by observing the 

 positions taken by those coming from the seeds r\ the preceding 

 experiment, and also by placing the stems of growing plants in new 

 positions. Select three small similar plants each with a single actively 

 growing stem, and place them in darkness in such positions that 

 their stems will point in the most different possible directions, and 

 observe results. 



(If the pots are to be turned upside down, the earth may be kept from 

 falling out by ccnu-rnig it li'it/i a ivad of sphagnum held in place by 

 strings across the pot. 



80. When the direction of growth is once determined, is it 

 held regardless of external conditions, or does it continue respon- 

 sive to the original condition determining it? 



Answer by Experiment 46. 



EXPERIMENT 46. This may be tested by changing the positions 

 of roots after thev have attained to some size. After the roots in 



j 



Experiment 44 have reached a length of two or three inches, and 

 side roots have appeared, turn the box in the plane of the glass 

 through 45, and observe effect upon the position of the old and 

 the new roots. 



Also, after the stems of Experiment 45 have shown their complete 

 result, restore them to their former positions. 



The results of the preceding experiments show not only 

 that roots and stems take definite positions in growth which 

 are independent of the position of the seed or plant from which 

 they arise, but also that unequal distribution of light, heat, 

 moisture, etc., cannot be the influence which guides them into 

 those positions. The suggestion then arises that their position 

 is perhaps connected with the "up-and-down' direction, 

 which of course is determined solely by gravitation. Obviously 

 this hypothesis could be tested if a set of growing parts, with 

 other conditions as in the preceding experiments, could be 

 removed from the influence of gravitation. 



81. What is the effect upon the position of roots, when, with 

 other conditions as uniform as possible, gravitation is not allowed 

 to act upon growing seeds ? 



Answer by Experiment 47. 



EXPERIMENT 47. Since nothing on the earth's surface can be re- 

 moved from the influence of gravitation, the only way in which it can 



