350 BOTANICAL GAZETTE [May 
it tends to produce distortion in the roots after 12 to 15 hours 
of 23° or over. This may come from the lack of oxygen or the 
accumulation of the excreta of the root. The experiments 
recorded above, therefore, were performed with open tubes, 
except for the narrowing at the inner ends, as shown in fig. 15. 
The tips of the roots in all the experiments were kept from 5 to 
15™" removed from the lower open ends of the tubes. In 
several tests where the whole root was enclosed in a tube, the 
tip coming even with the lower open end, there was no curva- 
ture. The possibility, therefore, of curvature being caused by 
streams within the tubes may be dismissed. 
The experiments show a decreasing sensitiveness in the roots 
from the region of the elongating zone back to a position at least 
15™" from the apex. When 20™" of the apex of the root were 
covered there seemed to be some disturbance of the root but no 
Pronounced directive influence. There were in this case pro- 
portionately more than twice as many negative curves as in any 
other set, while the number of positive curves was much less — 
than in other experiments, ae 
It is worth noting that the percentages of positive curvature — 
in the four different sets show a constant decrease, being 80 oe 
cent. in roots with 3 to 8™" covered, 71 per cent. in ilacsce un 
To™" covered, 44 per cent. in roots with 15™™” covered, and 32 a 
per cent. in roots with 20™ covered. The angles attained - 
_ these curvatures were often as great as the tubes would — 
and averaged 17° in the first series, Ig° in the second, 18° 0 2 
the third, and 11° in the fourth. Thus it is shown that when ° 
z20™" of the root were covered the positive response? a oS 
relatively so few and gave such small angles that one may Ae 
suppose that the limit of sensitiveness has been eee 
Not so, however, with the portion of the radish root 5 ae - 
the tip; of the twenty-three seedlings used, nearly espace 
good positive curves, and there were only two nega 
The small number of negative curves is excellent ¢ idence 
the reliability of the result; for the absence of ne ae 
shows that the positive curves cannot be charged to patholon™ 
distortion. : a. 
