1902] THE RHEOTROPISM OF ROOTS 
hours. Of the twenty-three roots, ten became positive, two 
negative, and eleven remained neutral. ; 
_ Two experiments, including nineteen seedlings, were made, — 
inwhich 20™ of the apex of the roots were covered, and the | 
toots left exposed for 5 to 8™™ above this portion. One experi- 
ment ran for 9 hours, the other for 11 hours. Of the nineteen 
foots, seven became slightly positive, four slightly negative, and. 
‘tight remained straight. oe 
The results here recorded are most interesting. They teach 
that the root is sensitive to the rheotropic stimulus at a con- 
‘Siderable distance back of the elongating zone. The elongating — . 
tne in this variety of Raphanus sativus extends but 5™™ back of 
the tip. This fact I determined by marking ten roots with India - 
nk, and observing them with a horizontal microscope at inter- 
vals during 24 hours. The roots were kept immersed in water. - 
‘owth was observed to take place in some roots in the first 
il only, and in the others in the first 5™™. No root showed 
‘longation of the sixth millimeter. All conditions for 
fowth were favorable, and good growth took place io 
Objectionable conditions were in these experiments rem : 
Possible. The experiments were all performed wit 
(of five weeks, the temperature was held within a varia 
Me Thus it would seem 
“Y Of a current within the tubes was exclud 
‘OF the ends of the tubes is, however, not advise 
