548 
NATURE 
[Jury 23, 1914 
even in small quantities, is fatal to the plant. Chloro- 
form acts as a strong narcotic, inducing a rapid 
abolition of excitability. |The ludicrously unsteady 
gait of the response of plant under alcohol could be 
effectively exploited in a temperance lecture! The 
record (Fig. 5) is in the nature of an anticlimax, where 
the plant has drunk (pure water!) not wisely but too 
well. The gorged plant is seen to have lost all power 
of movement. I was, however, able to restore the 
plant to normal condition by extracting the excess of 
liquid by application of glycerin. 
Fic. 5.—Abolition of motile excitability by excessive absorption 
of water, and subsequent restoration by withdrawal of excess. 
It may be urged that the various reactions of irrit- 
ability may hold good only in the case of the particular 
plant Mimosa, and that the majority of plants were 
quite insensitive. I have, however, been able to demon- 
strate in this very hall thirteen years ago, through my 
discovery of electric response in ordinary plants, that 
every plant and every organ of the plant is sensitive.? 
The difficult problem of finding the time taken by the 
plant to perceive and respond to a blow was solved by 
the employment of my resonant recorder, in which 
the writer was tuned to vibrate two hundred times a 
second. The successive dots are thus at intervals of 
1/200 part of a second apart. Ina 
particular experiment there are 15-2 
intervals between the application of 
stimulus, represented by a vertical 
line, and the initiation of response 
(Fig. 6). The latent period, there- 
fore, in this case is 0-076 of a 
second. The reaction time of the 
plant becomes very sluggish under 
fatigue. 
Excitatory Impulse in Mimosa. 
I next take up the question of 
transmission of excitation in plants. 
It has hitherto been supposed in 
Mimosa the impulse caused by irri- 
tation is merely hydro-mechanical, 
and quite different from the nervous 
impulse in the animal. According to this hydro- 
mechanical theory, the application of mechanical 
stimulus is supposed to squeeze the tissue, in conse- 
quence of which the water forced out delivers a 
mechanical blow to the contractile organ of the plant. 
Such hydromechanical transmission is in no way 
affected by any physiological agencies as warmth or 
cold, or the application of various anzesthetics or 
poisons. 
In strong contrast to this is the transmission of 
2 ate : 3 
* Bose: Friday evening discourse, May 10, root. 
NO. 2334, VOL. 931] 
Fic. 6.—Record showing the latent period of Mimosa. 
The time-interval between successive dots is here o’oo05 sec. 
nervous impulse, which is a phenomenon of passage 
of protoplasmic disturbance from point to point. Here 
under favourable physiological conditions, such as 
warmth, excitatory impulse is transmitted with a 
quicker speed. There are certain agents again which 
paralyse the conducting tissue for the time being, 
causing a temporary arrest of the impulse. Such 
agents are known as anesthetics. There may again 
be poisonous drugs which permanently abolish the 
conducting power. The nature of an impulse may 
thus be discriminated by several crucial tests. The 
impulse must be physiological, or of a nervous char- 
acter, if physiological changes affect the rate of con- 
duction; absence of such effect, on the other hand, 
proves the mechanical character of the impulse. 
Of the various physiological tests, Pfeffer employed 
that of the narcotic drug. Chloroform applied on the 
surface of the stem of Mimosa failed to arrest the 
impulse. This result, at first sight, appears most 
convincing, and has been universally accepted as a 
disproof of the existence of nervous impulse in 
Mimosa. A little reflection will, however, show that 
under the particular conditions of the experiment, the 
conducting tissue in the interior could not have been 
affected by the external application of the narcotic, 
the task being, in fact, as difficult as narcotising a 
nerve-trunk lying between muscles by the application 
of chloroform on the skin outside. 
The question of nervous impulse in plants has thus 
to be attacked anew, and I have employed for this 
purpose twelve different methods. They all prove con- 
clusively that the impulse in the plant is identical in 
character with that in the animal. Of these I shall 
give a short account of two ditferent modes of inves- 
tigation. It is obvious that the transmitted impulse 
in Mimosa must be of an excitatory, or nervous 
character :— 
(1) If it can be shown that physiological changes 
induce appropriate variation in the velocity of trans- 
mission of the impulse. 
(2) If the impulse in the plant can be arrested by 
different physiological blocks by which nervous impulse 
in the animal is arrested. 
For the last two investigations the research resolves 
itself into the accurate measurement of the speed with 
which an impulse in the plant is transmitted, and the 
The recorder vibrates 200 times per second. 
variation of that speed under changed conditions. A 
portion of the tissue at C may, for example, be sub- 
jected to the action of cold, or of a poisonous drug 
(Fig. 7). In order to find the speed of normal trans- 
mission, we apply an instantaneous stimulus, say, of 
an electric shock, at B, near the pulvinus. <A short 
interval, the latent period, will elapse between the 
application of stimulus and the beginning of respon- 
sive movement. After the determination of the latent 
period, we apply stimulus once more at A, and observe 
the time which elapses between the application of 
ae 
