43 2 Newcombe . — The Sensory Zone of Roots. 
seedlings passed into these, and wet cotton was used as 
packing to fix the seedling in the tube. The preparation is 
illustrated in Fig. 24 (I). 
The seedlings with encasing tubes were secured to a bar 
of white pine 20 cm. in length, the bar was adjusted parallel 
with the diameter and just above the water of a glass basin 
22 cm. in width. The roots and glass-tubes project into the 
water. The seedlings were now adjusted to the proper ex- 
posure of apex by moving them up or down the tubes, and 
the basin of water was set revolving. Such a preparation as 
this needs almost constant watching, for the growth of the 
roots necessitates the raising of the seedlings in the tubes at 
intervals of fifteen to thirty minutes. 
Tested by this method, Zea Mays (popcorn), when only 
1 mm. to 2 mm. was exposed to the action of the stream, 
gave nine positive curves out of a total of twenty-one roots, 
the twelve remaining neutral. The period of the experiment 
was only four hours in one case and eight hours in the other, 
thus accounting for the small number of curves. Since there 
were no negative curves, however, the positive ones may be 
counted as irritable responses. In a later experiment with 
the same species, ten roots were in the water-stream for seven 
hours with never more than 1*5 mm. exposed beyond the 
glass-tubes. Six positive curves resulted, and four roots 
remained straight. 
Raphanus sativus tested by the foregoing method, with not 
more than 2 mm. of apex exposed, the duration of the experi- 
ment being six hours, gave positive responses in all of the 
thirteen roots used. In a second similar experiment lasting 
for eight hours, with never more than 1-5 mm. being exposed, 
nineteen roots became positive and one remained neutral. 
In a third experiment lasting nine hours, in which nineteen 
seedlings were used, with never more than 1 mm. of the root- 
apex exposed, eleven roots became positive, while the other 
eight remained neutral. 
Since the publication of the foregoing results a third species 
has been tested as were the two others, this being Brassica 
