292 ScCHREINER AND REED: EXCRETIONS BY ROOTS 
prepared agar. Sixteen of these roots curved and grew out of the 
tubes into the freshly prepared agar. The proportion of the 
response is 56: 100, which is almost precisely the proportion ob- 
tained where no precautions were taken to exclude bacteria. 
Hence it is believed that the results related in this paper are not 
induced (although they may be modified) by the action of bacteria. 
Experiments in which the attractive effect of gravity on the roots 
was neutralized. — It is evident to anyone familiar with the growth 
of roots that the positive geotropism, inherent in the wheat roots 
would hinder their lateral curvature and growth out of the tubes. 
The responses which have been thus far obtained are therefore the 
resultant responses to these two stimuli. One might expect that 
a root which was only feebly stimulated by the presence of the 
deleterious substances might be more strongly stimulated to grow 
downward by the attractive force of gravity and hence show no 
response. The action of gravity cannot be eliminated but it can 
be neutralized by revolving the plants so that all sides are equally 
stimulated. Accordingly in the subsequent experiments the pre- 
parations containing the seedlings were rotated by attaching them 
to the arms of a klinostat driven by a small electric motor. The 
dial which supported the arms was 25 cm. in diameter and revolved 
once in two minutes. The construction of klinostat and general 
method of use were similar to the type previously described by 
Reed ('03). 
In all the following experiments the segmented tubes were 
contained in glass vials 10 cm. long and 2.5 cm. in diameter. The 
vials were attached to the arms of the klinostat in such a way that 
they revolved in a plane perpendicular to their long axis. One 
wheat seedling was placed in each segmented tube and each experi- 
ment lasted several days, 
Three experiments were performed using freshly prepared 
agar, Out of a total of 47 roots, 31 curved and grew out of the 
segmented tubes, a response of 66 per cent. The response in 
similar tubes which had not been rotated had been 53 per cent. 
Summing up the results of these experiments, it appears that 
the roots of wheat seedlings are repelled by some deleterious sub- 
stance or substances produced during growth and that a satisfac- 
tory means of demonstrating the same is by the use of segmented 
