JuLy 23, 1914] 
NATURE 
549 
stimulus and the response. The difference between 
the two periods 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 obtain the speed of impulse in the plant. The 
experiment is repeated once more, after the applica- 
tion of a given agent at C. If the speed undergoes 
any variation, it must be due to the action of the 
given agent. 
Fic. 7.—Experimental arrangement for determination of velocity of trans- 
mission and its variation. Record is first taken when stimulus is applied 
near the pulvinus at B (latent period) and then at a distant point on the 
leaf-stalk at A. Difference of two gives time for transmission from A to 
B. The band of cloth C is for local application of warmth, cold, anzs- 
thetics, and poison. 
Determination of Speew of Excitatory Impulse in 
Plants.* 
As relatively long intervals have to be measured in 
the determination of velocity, the recorder has its 
frequency adjusted to ten vibrations per second; hence 
the space between successive dots represents an in- 
terval of one-tenth of a second. In Fig. 8 is given 
a record for determining the velocity of transmission. 
The two 
Fic. 8.—Determination of velocity of transmission in Mimosa. 
lower records are in response to stimulus applied at a distance of 30 mm. ; 
the upper record exhibits latent period in response to direct stimulus 
applied on the pulvinus. Successive dots in this and following records 
are of intervals of one-tenth part of a second. 
The two lower figures give practically identical results 
of successive experiments when stimulus was applied 
at a distance of 30 mm. _ The uppermost is the record 
for direct stimulation. From these it is seen that the 
3 For a more detailed account consult :— 
Bose : ‘An Automatic Method for the Investigation of Velocity of Trans- 
mission of Excitation in Mimosa.” Phil. Trans. Royal Society, Series B, 
vol. cciv. 
Rose: ‘‘ Plant Response.”” (Longmans, Green, 1906). 
Bose: ‘‘ Researches on Irritability of Plants.” (Longmans, Green, 1913.) 
No.8 2334, VOL. 93) 
} 
| 
| leaflets of which dance up and down. 
| 
interval between stimulus and response is 1-6 seconds, 
and that the latent period is o-1 second. Hence the 
true time for the excitation to travel through a dis- 
| tance of 30 mm. is 1-5 seconds, the velocity being 
20 mm. per second. 
The velocity of nervous impulse in the plant is 
slower than those of higher, but quicker than those of 
lower animals. The speed of the impulse is, however, 
subject to variation under different conditions. One 
significant result that came out was that while a plant 
carefully protected under glass from outside blows 
looked sleek and flourishing, yet as a complete and 
perfect organism it proved to be a failure. Its con- 
ducting power was found atrophied or paralysed. 
But when a succession of blows rained on this effete 
and bloated specimen, the stimulus canalised its own 
path of conduction, and it became more alert and 
responsive, and its nervous impulses became very 
much quickened. 
Effect on Physiological Agencies on Velocity. 
A decisive experiment to discriminate between the 
theories of mechanical and nervous transmissions, 
consists in the determination of the effect of tempera- 
ture on the speed of transmission. Temperature has 
no effect on mechanical propagation, whereas a 
moderate variation of it profoundly affects the rate of 
nervous transmission. In the case of the plant, I find 
that the velocity is doubled by rise of temperature 
through 9° C. When a portion of conducting petiole 
is subjected to cold the speed of conduction is re- 
tarded. Excessive cold temporarily abolishes the con- 
ducting power. 
As an after-effect of the application of intense cold, 
the conducting power remains paralysed for a con- 
siderable length of time. It is a very interesting and 
suggestive fact that I have been able to restore the 
conducting power quickly by subjecting the paralysed 
portion of the plant to a measured and moderate dose 
of electric shock. 
Various physiological blocks can be made to inhibit 
the excitatory impulse in the plant, precisely as in the 
case of animal nerve. The nervous impulse in plants 
may thus be arrested by electrotonic block or by the 
action of poisons. By applying solution of potassium 
cyanide I have been able to abolish the conducting 
power in the plant in a time as short as five minutes. 
This investigation on the simplest type of plant-nerve 
is expected to cast a flood of light on the very obscure 
phenomenon of nervous impulse in general, and the 
causes operative in bringing about the degeneration 
of the normal function of the nerve. 
Spontaneous Pulsation. 
In certain animal tissues, a very curious pheno- 
menon is observed. In man and other animals, there 
are tissues which beat, as we say, spontaneously. 
So long as life lasts, so long does the heart continue 
to pulsate. There is no effect without a cause. How 
then was it that these pulsations became spontaneous ? 
To this query, no fully satisfactory answer has been 
forthcoming. We find, however, that similar spon- 
taneous movements are also observable in plant 
tissues, as in D. gyrans, or the telegraph plant, the 
The character- 
istics of the automatic pulsations in the plant could 
not be determined on account of the apparent impossi- 
bility of obtaining a record. The leaflets are too 
minute and the pull exerted too feeble to overcome 
friction of the recording surface. This difficulty has 
been obviated by the device of my oscillating re- 
corder (see pulse-record, Fig. — 9). From the 
records thus obtained, I am enabled to say that the 
automatic movements of both plants and animals are 
guided by laws which are identical. Thus I find, as 
