102 Newcombe, Gravitation sensitiveness not confined to apex of root. 



Experimental. 



To test the geotropic sensitiveness of beheaded roots, resort 

 was had to the centrifuge. An electric motor was used jto drive 

 several horizontal shafts, each shaft having at one end a heavy 

 brass disk, to which by simple means a glass basin 22 cm in di- 

 ameter could be secured. These glass-basins were used as damp- 

 chambers, being lined with filter paper, and so covered with a 

 heavy giass plate clamped over a thick rubber disk that after 

 even 24 hours of revolution there was always free water remaining in 

 the Chamber. In the damp-chamber there was fltted a wooden cross 

 of2bars, the bars occupying the position of diameters at right angles 

 to each other. The wooden cross was easily removable and to it, 

 perpendicularly to the diameters, were fastened the seedlings by 

 means of strips of cloth and rubber bands. Such a preparation ?is 

 shown in Plate III. The motor was so geared to the shafts turning 

 the damp-chambers that the revolution was 300 times a minute. 

 Such a revolution gives approximately as many times the acceleration 

 of gravitation as the root-tips are distant in centimeters from the 

 center of revolution. Nearly all the experiments were conducted 

 with an acceleration equal to 7 g or 8 g. By the method indicated 

 one could easily secure accelerations all the way from 1 g to 10 

 g in one preparation. 



To insure accuracy in the length of root-tips excised and in 

 cutting perpendicularly to the long axis of the root, a little guillo- 

 tine was devised with guide posts for the razor and with a micro- 

 meter screw moving a little block back and forth, the root to be 

 cut having its tip placed against the block, the position of the 

 block determining the length of tip to be removed. This device 

 did excellent service, cutting the tips with an error of less 

 than one-tenth millimeter, end uniformly perpendicularly to the 

 axis of the root. 



The temperature during the experiments varied between 20° 

 and 24° C. The seedlings were kept in the normally vertical 

 position both before and after beheading, and never more than 

 10 minutes elapsed between the beheading and the beginning of 

 revolution. 



The seedlings employed were those of Zea mais, Lupmus 

 albus, Pisum sativum. Phaseolus muliflorus, Vicia faba, Ricinus 

 communis, and Cucurbita pepo. Several of these species showed 

 thebehavior recorded by Wiesner, but 3ofthem showed behavior 

 not before recorded, and some of them have been tested more 

 thoroly than any before for the limitations of sensitiveness, and 

 for other relations. 



Zea mais. Twenty-nine seedlings had each 2 millimeters 

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

 for 8 hours. Twenty roots curved outwards at angles varying from 

 10° to 25°, one root curved inward, and one curved in a direction 

 at right angles to the plane of revolution. The other seven 

 made no bend. 



