12 3 BOTANICAL GAZETTE [JANUARY 
Apparently he took cells at equal distances from the tip in the 
normal and in the curved roots; but cells so situated would be 
comparable only if the two roots elongated at the same rate after 
the stimulation of the one, and this rate is just the point to be 
proved. To assume it, therefore, is to beg the question. 
MacDougal’s results give further evidence that his ‘‘normal ” 
roots were not normal. In his tables IX and X he gives results 
with roots bent mechanically, one after being geotropically excited 
one hour, the other without excitation. This latter one (table 
IX) must have been normal up to the time of bending, and as 
the author says the cells of the convex side have enlarged and 
those of the concave side diminished, the latter cells ought to be 
shorter than normal, but the figures given show the cells of the 
concave side in the root bent mechanically to be five times as 
long as the cells in his “normal” root. In the roots mechanically 
bent the curve of shortest radius coincides with that in roots 
geotropically excited; hence the latter are comparable to the 
former, taking into consideration the time element. If there is 
as much elongation in the region of greatest curvature of geotropi- 
cally curved roots as ‘MacDougal supposes, those which are 
geotropically excited and then bent mechanically ought to have 
longer cells than those bent without excitation, as both were bent 
90°; but the figures show that, cells on the .concave side of 
roots stimulated before bending are little more than half as long 
as those bent without stimulation. Also the cells in the convex 
side of the former are only three fourths as long as those in the 
corresponding part of the latter. Looking at all the figures 
given by MacDougal, it is found that in all the roots curved 
geotropically the cells on the concave side are shorter than those 
on the same side of roots bent mechanically without stimulation ; 
this is true even for the curves one hundred hours old, though 
here the growing tip has advanced 3°™ beyond the curve of 
greatest radius. Even the cells of the convex side of roots curved 
geotropically are shorter than those on the corresponding side 
of the roots bent mechanically, except in those curves which 
were seventy and one hundred hours old. So far from admitting 
