The existence of such spontaneous movements can easily be demonstrated,
by means of our Indian _Bon charal_, the telegraph plant, or Desmodium
gyrans, whose small leaflets dance continually. The popular belief that
they dance in response to the clapping of the hands is quite untrue.
From readings of the scripts made by this plant, I am in a position to
state that the automatic movements of both plants and animals are guided
by laws which are identical.
Firstly, when, for convenience of experiment, we cut off the leaflet,
its spontaneous movements, like those of the heart, come to a stop. But
if we now subject the isolated leaflet, by means of a fine tube, to an
added internal pressure of the plant's sap, its pulsations are renewed,
and continue uninterrupted for a very long time. It is found again that
the pulsation frequency is increased under the action warmth, and
lessened under cold, increased frequency being attended by diminution of
amplitude and _vice versa_. Under either, there is temporary arrest,
revival being possible when the vapour is blown off. More fatal is the
effect of chloroform. The most extraordinary parallelism, however, lies
in the fact that those poisons which arrest the beat of the heart in a
particular way, arrest the plant--pulsation also in a corresponding
manner. I have thus been able to revive a leaflet poisoned by the
application of one, with a dose of a counteracting poison.
Let us now enquire into the causes of these automatic movements
so-called. In experimenting with certain types of plant tissues, I find
that an external stimulus may not always evoke an immediate reply. What
happens, then, to the incident energy? It is not really lost, for these
particular plant tissues have the power of shortage. In this way, energy
derived in various ways from without--as light, warmth, food, and so
on--is constantly being accumulated, when a certain point is reached,
there is an overflow, and we call this overflow spontaneous movement.
Thus what we call automatic is really an overflow of what has previously
been stored up. When this accumulated energy is exhausted, then there is
also an end of spontaneous movements. By abstracting its stored-up
heat--through the application of cold water--we can bring to a stop the
automatic pulsations of Desmodium. But on allowing a first accession of
heat from outside, these pulsations are gradually restored.
In the matter of these so-called spontaneous activities of the plant, I
find that there are two distinct types. In one, the overflow is
initiated with very little storage, but here the unusual display of
activity soon comes to a stop. To maintain such specimens in the
rhythmic condition, constant stimulation from outside is necessary.
Plants of this type are extremely dependent on outside influences, and
when such sources of stimulus are removed, they speedily come to an
inglorious stop. _Kamranga_ or _Averrhoa_ is an example of this kind. In
the second type of automatic plant activity I find that long continued
storage is required, before an overflow can begin. But in this case, the
spontaneous outburst is persistent and of long duration, even when the
plant is deprived of any immediately exciting cause. These, therefore,
are not so obviously dependent as the others on the sunshine of the
world. Our telegraph-plant, _Desmodium_ or _Bon charal_, is an example
of this.
It appears to me that we have here a suggestive parallel to certain
phenomena with which this audience will surely prove more familiar than
I, namely, the facts of literary inspiration. For the attainment of this
exalted condition, also, is it not necessary to have previous storage,
with a consequent bubbling overflow? Certain indications incline me to
suspect that perhaps in this also we have an example of so-called
spontaneity, or automatic responsiveness. If this be so, aspirants, to
the condition might well be asked to decide in whose footsteps they will
choose to tread--those of _Kamranga_, with its dependence on outside
influences, and inevitably ephemeral activity, or those of _Bon charal_,
with its characteristic of patient long enduring accumulation of forces,
to find uninterrupted and sustained expression.