times 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]

EXTENDED APPLICATION OF MECHANICAL THEORY

With an extended application of his mechanical theory, Dr. Bose has
gradually removed the veil of obscurity from many a phenomenon in plant
life. The 'autonomous' movements of plants, for example, which remained
enveloped in mystery, received a satisfactory solution at his hands.

'AUTONOMOUS' MOVEMENTS

It was believed that automatically pulsating tissues draw their energy
from a mysterious "vital force" working within. By controlling external
forces, Dr. Bose stopped the pulsation and re-started it and thus
demonstrated that the 'automatic action' was not due to any internal
vital force. He pointed out that the external stimulus--instead of
causing, as was customary to suppose, an explosive chemical change and
an inevitable run-down of energy--brings about an accumulation of energy
by the plant. And with the accumulation of absorbed energy, a point is
reached when there is an overflow--the excess of energy bubbles over, as
it were, and shows itself in 'spontaneous' movements. The stimulus being
strong a single response--a single twitching of the leaflets--is not
enough to express the whole of the leaf's responsive energy and it
yields a multiple response--it reverberates--it manifests itself in
'automatic' pulsations. When, however, the accumulat