1902] | THE RHEOTROPISM OF ROOTS 347 
tube never gave any curves. Contact with the side of the glass 
tube never effected any curvature. Scores of roots have been 
allowed to grow down through glass tubes, and many have by — 
filling with cotton been pressed against the tubes as the roots 
_§rew out through the lower end, yet none have curved in quiet 
Water. If we consider the proportion of the number curving to 
the total number of roots under experiment, we shall see that 
“there is no ground here for objection to the assumption of the 
_ Sesitiveness of the root-tip. In Zea mays almost half responded 
positively, and these were almost as many as have, in other 
experiments with the whole root uncovered, responded in the 
Sametime. In Raphanus sativus forty-three in fifty-two responded 
Psitively. That these curves were responses to the stream of 
_ Water is readily believed when it is seen that there was nota 
single case of a negative curve. The curves were all relatively 
va because the tubes stopped the progress of the curving oe 
curves were nevertheless decisive, being usually 15 to 20°, - 
‘to the author, who has during the past five years seen thou- ne 
“§ (Of irritable curves in roots, there can be no doubt of the 
rom the foregoing experiments it may safely be collin : 
t the apex of the root is sensitive to a rheotropic stimulus. 
9. Testing the sensitiveness of the root back of its apex. 
“order to determine what part of the elongating zone 
ih Sensitive, paired glass tubes constructed as shown 
used. The tubes were 30" in internal unre : 
ins together with fine annealed steel wire, and = a 
a Preceding group of experiments, and adjustments = 
desir ed €xposure of the root-surface were made as a 
oe seedling up or down in the tube. At mij 
=v: that the movement of seedlings up and down the 
interfere with results, either by injury to the roots OF 
a a different flank to meet the current. a ome sas 
