It was believed that so-called 'sensitive' plants alone exhibited
excitation by _electric response_. But Dr. Bose, believing in continuity
of responsive phenomena, used the same experimental devices, with which
he had already succeeded in obtaining the _electric response_ of
inorganic substances, to test whether ordinary plants also--meaning
those usually regarded as 'insensitive'--would or would not exhibit
excitatory _electrical response_ to stimulus. With the help of very
delicate instruments, Dr. Bose demonstrated the very startling fact
that not only every plant, but every organ of every plant gave true
_excitatory electric response_--and that response was not confined alone
to 'sensitive' plants like _Mimosa_.
Dr. Bose then proceeded to investigate whether the responsive effects
which he had shown to occur in ordinary plants might not be further
exhibited by means of _visible mechanical response_, thus fully removing
the distinction commonly assumed to exist between the 'sensitive' and
supposed 'non-sensitive.' Dr. Bose invented 'special apparatus of
extreme delicacy,' which detected infinitesimal tremors, and showed that
ordinary plants, usually regarded as insensitive, gave _motile
responses_, which had hitherto passed unnoticed. His later investigation
shows that "all plants, even the trees, are fully alive to changes of
environment; they respond visibly to all stimuli, even to the slight
fluctuations of light by a drifting cloud."[17]
'TROPIC' MOVEMENTS
Finding that the plants give, not only _electric_ but _motile_ response
as well, to stimulus, Dr. Bose proceeded to study the nature of
responses evoked in plants by the _stimuli of the natural forces_. He
found that plants respond visibly, by movements, to _environmental
stimuli_. But the movements induced--'tropic' movements--are extremely
diverse. Light, for example, induces sometimes positive curvature,
sometimes negative. Gravitation, again, induces one movement in the
root, and the opposition in the shoot. Dr. Bose applied himself to find
out whether the movements in response to external stimuli, though
apparently so diverse, could not be ultimately reduced to a fundamental
unity of reaction. As a result of a very deep and penetrating study of
the effects of various environmental stimuli, on different plant organs,
he showed that the cells on two sides are unequally influenced, on
account of different external conditions, and contract unequally, and
hence the various movements are produced--that the many anomalous
effects, hitherto ascribed to 'specific sensibilities,' are due to the
'differential sensibilities'--differential excitability of anisotropic
structures and to the opposite effects of external and internal
stimuli--that all varieties of plant movements are capable of a
consistent mechanical explanation. Dr. Bose's "latest investigations
recently communicated to the Royal Society have established the single
fundamental reaction which underlies all these effects so extremely
diverse."[18]