Again, just as, in following up light from visible to invisible, our
range of investigation transcends our physical sight, so also does our
power of sympathy become extended, when we pass from the voiced to the
unvoiced, in the study of life: Is there then any possible relation
between our own life and that of the plant world? That there may be such
a relation, some of the foremost of scientific men have denied. So
distinguished a leader as the late Burdon-Sanderson declared that the
majority of plants were not capable of giving any answer, by either
mechanical or electrical excitement, to an outside stock. Pfeffer,
again, and his distinguished followers, have insisted that the plants
have neither a nervous system, nor anything analogous to the nervous
impulse of the animal. According to such a view, that two streams of
life, in plant and animal, flow side by side, but under the guidance of
different laws. The problems of vegetable life are, it must be said,
extremely obscure, and for the penetrating of that darkness we have long
had to wait for instruments of a superlative sensitiveness. This has
been the principal reason for our long clinging to mere theory, instead
of looking for the demonstration of facts. But to learn the truth we
have to put aside theories, and rely only on direct experiment. We have
to abandon all our preconceptions, and put our questions direct,
insisting that the only evidence we can accept is that which bears the
plant's own signature.
How are we to know what unseen changes take place within the plant? If
it be excited or depressed by some special circumstance, how are we, on
the outside, to be made aware of this? The only conceivable way would
be, if that were possible, to detect and measure the actual response of
the organism to a definite external blow. When an animal receives an
external shock it may answer in various ways if it has voice, by a cry;
if it be dumb, by the movement of its limbs. The external shock is a
stimulus; the answer of the organism is the response. If we can find out
the relation between this stimulus and the response, we shall be able to
determine the vitality of the plant at that moment. In an excitable
condition, the feeblest stimulus will evoke an extraordinarily large
response: in a depressed state, even a strong stimulus evokes only a
feeble response; and lastly, when death has overcome life, there is an
abrupt end of the power to answer at all.
We might therefore have detected the internal condition of the plant,
if, by some inducement, we could have made it write down its own
responses. If we could once succeed in this apparently impossible task
we should still have to learn the new language and the new script. In a
world of so many different scripts, it is certainly undesirable to
introduce a new one! I fear the Uniform Script Association will cherish
a grievance against us for this. It is fortunate however that the
plant-script bears, after all, a certain resemblance to the
Devanagari--inasmuch as it is totally unintelligible to any but the very
learned!
But there are two serious difficulties in our path; first, to make the
plant itself consent to give its evidence; second, through plant and
instrument combined, to induce it to give it in writing. It is
comparatively easy to make a rebellious child obey: to extort answers
from plants is indeed a problem! By many years of close contiguity,
however, I have come to have some understanding of their ways. I take
this opportunity to make public confession of various acts of cruelty
which I have from time to time perpetrated on unoffending plants, in
order to compel them to give me answers. For this purpose, I have
devised various forms of torment,--pinches simple and revolving, pricks
with needles, and burns with acids. But let this pass. I now understand
that replies so forced are unnatural, and of no value. Evidence so
obtained is not to be trusted. Vivisection, for instance, cannot furnish
unimpugnable results, for excessive shock tends of itself to make the
response of a tissue abnormal. The experimental organism must therefore
be subjected only to moderate stimulation. Again, one has to choose for
one's experiment a favourable moment. Amongst plants, as with ourselves,
there is, very early in the morning, especially after a cold night,
certain sluggishness. The answers, then, are a little indistinct. In the
excessive heat of midday, again, though the first few answers are very
distinct, yet fatigue soon sets in. On a stormy day, the plant remains
obstinately silent. Barring all these sources of aberration, however, if
we choose our time wisely, we may succeed in obtaining clear answers,
which persist without interruption.
It is our object, then, to gather the whole history of the plant, during
every moment between its birth and its death. Through how many cycle of
experience it has to pass! The effects on it of recurring light and
darkness; the pull of the earth, and the blow of the storm; how complex
is the concatenation of circumstances, how various are the shocks, and
how multiplex are the replies which we have to analyse! In this vegetal
life which appears so placid and so stationary, how manifold are the
subtle internal reactions! Then how are we to make this invisible
visible?