GROWTH AND MOVEMENT 433 
cease entirely. When the stimuli recur very frequently, the responses 
become for a time combined, so that the organ assumes a fixed position 
unlike the unstimulated one. This quite resembles the condition of a 
muscle in tetanus, as can be seen by comparing the records in fig. 672. 
After a period of tetanus, however, the reactions cease until rest from 
excitation permits recovery. If stimulation, too brief to produce the 
FIG. 671. Uniform electrical response in radish to repeated stimulation. After BOSE. 
end reaction, be repeated at proper intervals, the separate effects be- 
come combined and suffice presently to call forth the end reaction. 
This summation of stimulation seems to be a sort of tetanic piling up of 
the earlier excitations of the series, which finally becomes sufficient to 
transmit its effects to the active region. 
a b 
FIG. 672. Records of tetanic contraction in muscle (a, 6) and in style of Datura (c, d) : 
a, c, incomplete ; b, d, more complete. After BOSE. 
Reaction time. Some time elapses between the beginning of stimu- 
lation and the end reaction, and this is appropriately called reaction 
time. Whereas in animals this is usually measured by a fraction of a 
second, in plants it is much longer, occasionally a few seconds, but often 
minutes or even hours. This tardiness is due not so much to a low 
degree of sensitiveness, for the first reaction (perception) takes place 
almost instantly, as to slow propagation and especially to the sluggish- 
ness of the mechanism of growth. By contrast, turgor mechanisms usu- 
ally respond quickly. Naturally the reaction time is made up of the 
perception time (a small fraction of a second), the transmission time (the 
rate varies commonly from o to 4 cm. per second), and the growth time, 
which is far the greater part of the whole period. 
