436 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1914. 
condition. A portion of the tissue at C may, for example, be sub- 
jected to the action of cold or of a poison (fig. 12). In order to find 
the speed of normal transmission, we apply an instantaneous stimu- 
lus, say, of an electric shock, at B, near the pulvinus. A short inter- 
val, the latent period, will elapse between the application of stimulus 
and the beginning of responsive movement. After the determina- 
tion of the latent period we apply stimulus once more at A and 
observe the time which elapses between the application of stimulus 
and the response. 
The difference be- 
tween the two pe- 
riods gives us the 
time required for 
the excitation to 
travel from the point 
of application of 
stimulus at A to the 
responding organ at 
B. Hence we ob- 
tain the speed of im- 
Fic. 13.—Determination of velocity of transmission in Mimosa. _ ul : i 1] 
The two lower records are in response to stimulus applied at a dis- puise im the p ant. 
tance of 30 mm.; the upper record exhibits latent period in response ‘(he experiment is 
to direct stimulus applied on the pulvinus. Successive dots in this 
and following records are of intervals of one-tenth part of a second. repeated once more 
after the application 
of a given agent at C. If the speed undergoes any variation, it must 
be due to the action of the given agent. 
DETERMINATION OF SPEED OF EXCITATORY IMPULSE IN PLANTS.* 
As relatively long intervals have to be measured in the determina- 
tion of velocity, the recorder has its frequency adjusted to 10 
vibrations per second, hence the space between successive dots 
represents an interval of one-tenth of a second. In figure 13 is 
given a record for determining the velocity of transmission. The 
two lower figures give practically identical results of successive 
experiments when stimulus was applied at a distance of 30 millimeters. 
The uppermost is the record for direct stimulation. From these it 
is seen that the interval between stimulus and response is 1.6 seconds, 
and that the latent period is 0.1 second. Hence the true time for 
the excitation to travel through a distance of 30 millimeters is 1.5 
seconds, the velocity being 20 millimeters per second. 
1 For a more detailed account confer: 
Bose, An automatic method for the investigation of velocity of transmission of excitation in Mimosa 
Phil. Trans. of Royal Society, Series B, Vol. 204. 
Bose, Researches on irritability of plants (Longmans Green, 1913). 
