N"ewcombe, Graritation sensitiveness not confined to apex of root. 103 



Thirteen seedlings had 2 . 5 mm excised, were revolved 

 at 8 g for 8 hours, and then showed 4 roots with outward curves 

 of 10° to 15°. The other 9 roots remainecl straight. In both 

 this and the preceding experiment all roots elongated after 

 beheading. 



These 2 experiments indicate very clearly that with 2.5 mm 

 of the root-tip removed, the root has in most cases lost the ability 

 to respond to the centrifugal force, while that ability is retained 

 generally when only 2 mm are excised. This lessening of the 

 response, must depend, if the curves are geotropic, on the relation 

 between the autotropism of the root and its geotropism, the latter 

 being reduced either by an increasing inhibition from more proxi- 

 mal wounding, or by a greater loss of sensory tissue, or by the 

 Operation of both factors. 



Pisum sativum. Fifteen seedlings had each 2 mm of the 

 tip removed, and were revolved on the centrifuge at 7 g to 8 

 g for 14 hours. Ten roots curved outwards forming angles of 

 10° to 30°, one root bent inward, two bent obliquely and two 

 grew straight. 



Forty-two seedlings with 2.5 mm of the root excised, re- 

 volved at 8 g for 8 hours, showed 13 roots bent outward at angles 

 from 10° to 30°, and 3 roots bent irregularly, the remaining 26 

 roots being straight. 



Five seedlings had 3 mm cut from the tip of the root, were 

 revolved at 8 g for 19 hours, and then .showed 4 weak outward 

 curves of 10° to 15°, and one weak inward curve. 



The teaching here is the same as for Zea mais. When only 

 2 mm were excised the responses in the same period were 

 proportionately more than twice as numerous as when 2.5 mm 

 were excised. 



The result when 3 mm were excised cannot be compared 

 directly with the others, for the period of revolution was more than 

 twice as great. The angles attained here were, however, considerably 

 weaker than in the other experiments. However, the result shows 

 that with even 3 mm of the tip removed, the roots still have the power 

 to respond to centrifugal force. 



Lupinus albus. In a total of 37 seedlings, from whose roots 

 2 mm had been cut, revolving at 8 g for 6 hours, 13 bent outward 

 (unfortunately my notes fail to give the angles), 4 bent irregularly, 

 and 20 grew straight. 



In a total of 34 seedlings from whose roots 2.5 mm 

 had been cut, revolving at 8 g for 7 hours, 10 bent out- 

 ward at angles from 10 ° to 60 °, 2 bent irregularly, and 22 grew 

 straight. 



The results here given do not certainly show that a grea- 

 ter inability to respond to centrifugal force is manifest the 

 greater the amount of the root excised. Farther experiments 

 are needed. 



PJuiseolus multiflorus. Only 8 seedlings were used to test 

 the effect of removing 2 mm of the root-tip, and these gave only 



