SCHREINER AND REEp: EXCRETIONS BY ROOTS 289 
curve and grow out of the narrow openings between adjoining 
segments of the tube. 
The first experiment employed a total of 26 roots. The jars 
containing the tubes and seedlings were wrapped in black paper 
and stood in a well lighted portion of the laboratory. At the 
expiration of 6 days, it was found that 14 of the roots had turned 
from their normal downward course and grown out through the 
Narrow openings into the surrounding agar. The experiment was 
repeated three times, using a total of 90 roots, 48 of which grew 
out of the tubes through the narrow openings. It will be noted 
that this is a response of 53 per cent. of the roots employed. 
Since the wheat roots are positively geotropic and possess 
thereby a natural tendency to grow vertically downward, it must 
be assumed that there was some definite stimulus acting at the 
Narrow openings of the segmented tubes which caused them to 
curve and grow out. The roots in these and later experiments 
showed no distortion nor traumatic curvatures. They always 
grew straight until reaching the openings through which they 
passed out into the surrounding medium, 
It seems justifiable, therefore, to conclude that their curvature 
Was a response to the presence of some substance or substances to 
which they were negatively chemotropic. Inside the narrow tube 
these substances were comparatively concentrated, but at the 
narrow openings the deleterious substances had partially diffused 
toward the exterior. When the roots reached the regions from 
Which diffusion had taken place they responded by curving and 
§fowing out of the tubes. The same phenomenon of diffusion 
will explain why the roots did not find the agar in the lower part 
of the tubes as favorable for growth as that outside the tube. 
The following experiment may be cited in further support for 
the above statements : 
Several jars containing melted agar, which had cooled to 36°- 
38° C., were thickly planted with wheat seedlings. In a few days 
the roots of the seedlings completely permeated the masses of 
‘gar, they were allowed to grow for a week longer and then care- 
fully pulled out, removing as little agar as possible. The agar 
Was melted over a steam bath at a temperature of 7 ape o 
filtered through absorbent cotton and poured into clean jars. 
