102 Newcombe, Gravitation sensitiveness not confined to apex of root. 
Experimental. 
To test tlie geotropic sensitiveness of beheaded roots, resort 
was had to the centrifnge. An electric motor was used to 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 rnbber disk that after 
even 24 hours of revolution there was always free water remaining in 
the Chamber. In the damp-chamber there was fitted a wooden cross 
of 2 bars, 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 seedhngs by 
means of strips of cloth and rnbber bands. Such a preparation ns 
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 miUimeter, end uniformly perpendicularly to the 
axis of the root. 
The temperature during the experiments varied between 20° 
and 240 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, Lupiniis 
albus, Pisum sativum. Phaseolus muliflojms, Vicia faba, Ricinus 
communis, and Cucurbita pepo. Several of these species showed 
thebehavior recorded by Wiesner, but 3 of them 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 varyingfrom 
10° to 250 , one root curved inward, and one curved in a direction 
at right angles to the plane of revolution, The other seven 
made no bend, 
