432 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1914. 
that this view is quite erroneous. In Mimosa diffuse stimulation 
causes relatively greater contraction of the more excitable lower half 
of the pulvinus, and this differential action is magnified by the long 
petiolar index. Had the upper half of the pulvius been equally 
excitable as the lower, then the antagonistic reactions would have 
balanced each other. In radial organs we do not observe any lateral 
movement asin Mimosa. ‘This is not owing to insensitiveness, but to 
equal contractions on all sides balancing each other. The shortening 
of length of various radial organs like soft stem, tendril, pistil, and 
stamen, can easily be shown by means of magnifying levers. Again, 
if we take a hollow tubular organ of some ordinary plant, say the 
peduncle of daffodil, it is 
clear that the protected inner 
side of the tube must be the 
more excitable. When this 
is cut in the form of a spiral 
strip and excited by means 
of an electric shock, we ob- 
serve aresponsive movement 
by curling, brought about by 
greater contraction of the 
inside of the strip. If again 
we take a tendril which has 
curled round a support, the 
outside is fresh and free from 
Fic. 10.—Abolition of motile excitability by excessive irritation and therefore more 
absorption of water, and subsequent restoration by excitable. In this case the 
withdrawal of excess. : 5 
response is by uncurling, due 
to greater contraction of the more excitable outer side of the spiral. 
In the case of woody plants, responsive movement is prevented by 
the rigid support. Even in such a ease I have been able to demon- 
strate its excitation by means of electric response, first exhibited at 
this very hall 13 years ago.!’ No plant could appear more stolid and 
irresponsive than the common radish; appearances are, however, 
deceptive, and we find it giving a series of vigorous responses in answer 
to successive stimuli. The electric response comes to an end with 
the death of the plant. 
LATENT PERIOD OF PLANT. 
I next take up the very difficult problem of finding out how long 
it takes for the plant to perceive and respond to a blow. In attempt- 
1 Bose—Friday evening discourse, May 10, 1901. 
