- _ the narrowed opening. Inthe second experiment the ben 
346 BOTANICAL GAZETTE [May : 
in 5 hours ten were positive, and in 6 hours all thirteen were 
positive. These roots had never more than 2™" exposed. 
Another set of twenty seedlings with 1 to 1.5™ of the apex 
exposed gave, after 8 hours, nineteen roots decidedly positive 
and one neutral. In a third experiment, the roots had a maxi- 
mum of I™" exposed, each root being raised to 0.5™™ of exposed 
tip as soon as it approached the millimeter limit. Nine seedlings 
were used, and in g hours five roots had become positive, while 
the other four remained neutral. A final experiment, conducted 
exactly like the last, gave, after 9 hours, six roots positive with 
angles of 10 to 20°, while the other four roots remained neutral. 
Unless serious objection can be brought against these experi- 
ments, they prove that the apex of the root is sensitive to the 
rheotropic stimulus. It may be objected by some that too much 
of the root was exposed, so that the elongating zone was affected 
by the current. This stricture can hardly hold when we con 
sider that in one experiment with Za mays not more than 1.5" 
was exposed, and in two experiments with Raphanus sativus not 
more than 1™™ was exposed. The root cap of this hap . 
has an axial depth of 0.3 to 0.4™™, so that not more than 0.7— 
back of the cap was exposed, and this amount only for a small 
fraction of the period of the experiment. It may be thought : 
_ that possibly there was a current in the tube itself at a greater 
or less distance above its lower end. This objection has. 
answered, to some degree at least, by two devices: 
experiment the lower ends of the tubes were contra ot pi 
the root nearly filled the aperture; in the other experiment : . 
Space between root and tube was lightly filled with — 
both cases good curves were formed. In the first experi” of 
the bend in the roots took place above the constricted mown 
the tube, while the tip of the root extended obliquely ‘thee 
: Place in and below the cotton, the cotton not offering 
-Sreat resistance. Another answer to the foregoing ‘ 
_ lies in the fact that roots that were kept retracted bee 
: _ tubes so that their tips were level with the lower end 
