104 Newcombe, Gravitation sensiviteness not confined to apex of root. 



2 outward curves of 15° during a period of 6 hours. Two and 

 a half millimeters were cut from the tips of 45 roots and these 

 seedlings as the others were revolved for seven and one-half hours 

 at 7 g to 8 g. Among them, 13 roots curved outward at angles 

 varying from 15° to 45°, 3 roots bent inward, and the remaining 

 29 roots grew straight. 



These results may be accepted as demonstrating the ability 

 of the beheaded roots of this species to respond to the centrifugal 

 force, but the number of seedlings employed when 2 mm of the 

 root were excised was too few to allow comparisons to be made 

 with those from which 2.5 mm were removed. The large number 

 of seedlings used when 2.5 mm were removed and the resulting large 

 number of neutral roots makes certain the conclusion that, tho some 

 individuals so treated are capable of responding, the large majority 

 have lost that ability. 



Ricinus communis. Fifty-two seedlings with tips amputated 

 were revolved on the centrifuge at 8 g, temperature 20 ° to 22 ° C, 

 and period 6 to 8 hours. None of them showed curves that could 

 be called geotropic. All of the roots grew straight except 10 

 which curved but slightly in various directions. Twenty of these 

 roots had 3 mm excised, 13 had 2.5 mm excised, 13 had 2 mm excised, 

 and 6 had 1.5 mm excised. None of those in the last two groups 

 showed any curvature. 



This species is distinguished as the only one of the seven used 

 inthiswork which does not respond to centrifugal action when 1.5 to 

 2 mm of the root are removed. 



Vicia faba. The response of the roots of this seedling on the 

 centrifuge was determined by Wiesner as possible but infre- 

 quent when 3 mm were amputated. In my experiments a beginning 

 was made by amputating 2.5 mm, and subjecting the seedlings to a 

 speed of 8 g in temperature varying from 20 ° to 23 ° C. Fourteen 

 seedlings were revolved during 7 hours, and 8 curved outward at 

 angles ranging from 15 ° to 66 °, one curved toward the center and 

 five grew straight. 



When under the same conditions 41 seedlings were used 

 from which 3 mm of the root had been removed, 34 made 

 outward curves at angles ranging from 15 ° to 50 °, averaging 

 over 30°; only one root curved inward, while the other 6 

 grew straight. 



Forty roots had 3.5 mm of the tip removed, were revolved 

 at 8 g, in a temperature generally of 21 ° (for one set of 4 roots 

 it was only 14° C, but the period here was lengthened to 10 

 hours), for a period of 6 to 8 hours. Twenty-six roots bent out- 

 ward, one inward, 3 obliquely to the plane of revolution, and 10 

 grew straight. The angles formed by these roots averaged slight- 

 ly less than those formed by the roots which had but 3 mm am- 

 putated. See Plate ÜI for one set of these seedlings. 



Thirty-five roots had each 4 mm removed from the tip, 

 were revolved at 8 g, temperature was 20° to 23°, and the period 

 6 so 7 hours. Sixteen roots bent outward, and 19 g'rew straight, 



