THE RHEOTROPISM OF ROOTS 283 
. This phenomenon I have seen only in two con- 
been high temperatures when the growth was very rapid, 
d with a very weak stimulus, the latter illustrated in fig. 8, ¢. 
sh dea explained in either of two ways. We may suppose 
e root changes its sensitiveness or degree of response in 
ucce ve periods of time; or we may suppose that the after- 
efiect of the gravitation stimulus on the one hand, and of the 
tropic stimulus on the other alternately carries the bending 
root beyond the position of equilibrium, thus producing an oscil- 
back and forth over the position of equilibrium, the older 
of the curving portion being fixed at the two extremes of 
‘water iow a second response. If, owen a root 
its Sensitiveness or its ability to respond after losing 
ve might expect the appearance of such an a : 
— as that just described. 
[ Zo be concluded. | 
