New combe , — The Sensory Zone of Roots. 433 
alba , Boiss. Only eight seedlings were used ; the temperature 
of the water was 24°C. ; the velocity of the water-steam ranged 
from 200 cm. per minute for the roots nearest the centre to 
700 cm. for those most distant ; the duration of the test was 
six hours, and there was never more than 1 mm. of apex 
exposed. Seven roots showed strong positive curves, and 
the eighth was neutral. 
From the foregoing results there can be no doubt that the 
apex of these roots is rheotropically sensitive. 
III. Sensitiveness of the post-elongating Zone. 
It has already been shown 1 that the root of the seedling 
of Raphanus sativus is sensitive to a rheotropic stimulus 
from its apical millimetre back to at least the fifteenth milli- 
metre. Since the method in that study is the same as that 
used in the more recent testing of other species, it may be 
briefly summarized as follows : — Glass-tubing of 3 mm. internal 
calibre was cut into appropriate lengths, varying from 1 to 
3 cm., and paired tubes were made by joining two pieces 
together by fine annealed iron wire, as shown in Fig. 24(H). 
These tubes were washed in water for twenty-four or more 
hours before using. When the seedlings had attained a proper 
size, usually 3 to 5 cm. in length, the paired tube was filled 
with water, and the root of a seedling was passed in, the 
seedling being secured in the tube by packing wet cotton around 
the upper part of the root, or the lower end of the hypocotyl, 
as this was held in the upper section of the paired tube. 
A flattened needle with its point broken off did very good 
service in packing the cotton around the seedling. As each 
seedling was secured in a tube, the preparation was set 
vertically upright in a dish of water. Wlien ten such seed- 
lings were ready, a bar of wood about 1 cm. square and 20 cm. 
long was clamped in a vice at one end, and the glass-tubes 
with the contained seedlings were fastened to the bar. In 
fastening the preparations to the bar of wood, one side of the 
bar was first covered with wet blotting paper, the tubes were 
1 Newcombe, Bot. Gazette, xxxiii, 1902, p. 177. 
