312 New combe. — Geotropic Response at Various 
when the plant member was exposed to the gravitation stimulus at 135° 
from the position of normal equilibrium. Czapek attempted to use Sachs’ 
latent period method also for measuring relative geotropic response, but 
found the curves beginning in approximately the same time at all angles of 
inclination between 20° and 160 0 from the position of stable equilibrium. 
Stone l , in a very brief report of work with the roots of Vicia 
Faba and stems of grass, found the horizontal position to be the one of 
greatest response. He used dynamometers to measure the force of bending, 
measured the angles attained at different inclinations of plant axis, and 
compared the after-effect curvatures. 
A moment’s reflection over the results recorded in the foregoing 
abstracts of investigations will show one that the subject treated is left in 
a very unsatisfactory condition. In the first place, if it is conceded that 
a representative number of roots has been tested, the number of species of 
stems used is far too small. The hypocotyl of Helianthus , the stem of some 
grass, and the scapes of the cabbage and plantain alone have been tested. In 
the second place, the method employed to secure Czapek’s results — the most 
extensive work of all — seems to be open to several serious objections. The 
forcible retention of roots in glass tubes may, for ought we know, bring in 
traumatic phenomena. More serious still seems to me to be the consideration, 
the possibility of which must be admitted, that a weaker stimulus may accom- 
plish as much as a stronger one, provided the period of operation is long enough. 
That is to say, Czapek forced his roots to lie at their various angles of in- 
clination for three to six hours, a period far exceeding their latent period. 
It is easily conceivable that the gravitation-stimulus might in such a period 
effect the same result in roots stimulated at 90° and at 135 0 from their position 
of stable equilibrium, no matter which might be the angle of stronger 
stimulation, or stronger response under fairer conditions. One may question, 
too, whether the arbitrary selection of twenty-four hours as the period for 
the measurement of angles is likely to lead to reliable conclusions. 
With these thoughts in mind, but principally because stems had been 
insufficiently tested, Miss Haynes, in this laboratory, was assigned the 
subject of the angle of inclination of stems showing the strongest geotropic 
curvature, the test to be made by the method of alternate stimulation for 
a period less than the latent period, at angles of 90° and 135 0 from the 
position of stable equilibrium. 
This method of alternate or rhythmic stimulation on opposite sides of 
a plant member was used by F. Darwin and Pertz 2 in 1892. It has since 
been used in a modified way by various authors, among them Czapek 3 , 
1 ‘Geotropic Experiments.’ Bot. Gazette, xxix, 1900, p. 136. Abstract of paper read before 
Soc. Plant Morph, and Physiol., Dec., 1899. 
2 ‘ On the Artificial Production of Rhythm in Plants/ Annals of Bot., vi, 1892, p. 245. 
3 Ueber die Richtungsursachen der Seitenwurzeln und einiger anderer plagiotroper Pflanzentheile. 
Sitzungsber. d. k. Akad. d. Wiss., Math.-Naturw. Cl., civ, 1. Abt., 1895, p. 1197* 
