108 N^ewcombe, Gravitation sensitiveness not confined to apex of root. 
5 of the roots liad grown. and all were straight except oiie which 
had been able to make an ontward cnrve while still between 
tbe cork bars. 
The confining cork bars were now removed. and tbe preparation 
revolved for 2.5 boni^s longer at tbe rate of one revolution in 1.5 
ininntes. Observation tben sbowed tbat all 5 of tbe roots wbicb 
bad grown bad cnrved ontward at angles of 10 o. 15 o. 30 o. 45 ^ 
and 90° respectively. 
Tbirteen seedlings of Cucurbita pepo were treated preci- 
sely as tbe seedlings |in tbe preceding experiment, baving 3 
mm of tbe apex removed. and cork bars fastened on botb 
sides in contact witb tbe terminal 5 to 7 mm of tbe roots. 
Tbe speed was eqnal to 8 g, temperatiire 24.5°, and tbe 
period 7 bonrs. At tbe end of tbis period all 13 roots sbowed 
growtb, and were still confined between tbe cork bars, and 
were straigbt. On removal of tbe cork bars. 11 of tbe 13 roots 
immediateiy cnrved ontward at angles ranging from 15° to 70°, 
wbile tbe otber 2 remained straigbt. Tbe revolntion was imme¬ 
diateiy resiimed at tbe rate of once in 2 minntes, and after tbe lapse 
of 3.25 bonrs. tbe 2 roots formerly straigbt were cnrved at angles 
of 10° and 20° ontward, wbile one of tbe roots formerly cnrved 
ontward bad entmely straigbtened. Tbns all 13 roots bad sbown 
geotropic curves. 
Tbe metbod of experimentation bere presented is so simple 
tbat any one may follow it ont. Tbe only difticnlt step is tbe pro¬ 
per ampntation of tbe root-tips. If tbe experimenter will nse seed¬ 
lings of eitber Vicia faha or Cucurbita pepo. be cannot fail to ob- 
tain cnrves wbicb will convince bim tbat tbese plants possess gravi- 
tation sensitiveness in tbe part 4 millimeters distant from tbe apex, 
and even fartber. 
Tbe geotropic sensitiveness of tbe root, baving been, in 
my opinion, demonstrated to extend tbrongb 5 millimeters of 
some roots, we may now inqnire as to several geotropic cniwa- 
tnre-pbenomena wbicb present tbeniseves in various kinds of ex¬ 
perimentation. 
Bearing in mind tbe resnlts obtained witb tbe centrifnge, 
bow sball we offer an bypotbesis in accord botb witb tbem and 
witb tbe form of root-growtb illnstrated in Fig. 4. Tbe latter 
form is often seen witb Cucurbita pepo, Phaseolus multiflorus, Lu- 
pinus albus and Vicia faba wben one places seedlings of tbese 
species borizontally in a damp-cbamber. Tbe apex of tbe root. 
as far as tbe zone of maximnm growtb, declines 45° more or less. 
but tbe main direction of growtb is, in a considerable percentage 
of cases, horizontal or in a straigbt line dipping below tbe bori- 
zontal. Tbis form must be attained by tbe tissue of tbe decli- 
ning tip cbanging its direction as it passes bebind tbe zone of 
maximnm growtb. 
Tbere are two bypotbeses wbicb are in accord witb tbe 
pbenomena mentioned in tbe last paragrepb: (1) Tbe gratd- 
tation sensitiveness is strongest at tbe apex of tbe root and 
