References

3
Charles Darwin and the Plant Root Apex:
Closing a Gap in Living Systems Theory
as Applied to Plants
Peter W. Barlow
Abstract Charles Darwin was always pleased to exalt plants in the scale of organised beings,
drawing particular attention to the sensory properties of their roots. He even went so far as
to say that the root tip acts like a plant brain, located within the anterior end of the plant
body. What impressed Darwin was the ability of the root to perceive, often simultaneously,
multiple vectorial stimuli, and then make a ‘decision’ about which bending response to
follow. According to J.G. Miller’s ‘living systems theory’ (LST), developed mainly for human
organisms and human societies, there are similar sets of 20 subsystems supporting each
level of organisation, from cellular to organismic. If LST is a universal theory, it should
apply to plant organisms also. About half of all the LST subsystems concern the processing
of information. In the present plant-neurobiological context, the information-processing
subsystem of particular interest is ‘channel and net’. In the light of recent discoveries from
plant cell biology, earlier designations of structures to this subsystem are confirmed. They
reinforce the idea that plants possess a form of nervous system – even though Darwin denied
this particular proposition – which, moreover, makes use of molecules and organelles similar
to those found in the neurotransmission systems of animals. The LST approach to plant
life converges upon that already recognised for animals and, hence, provides a coherent
conceptualisation for the structuring of the two major kingdoms of plants and animals.
3.1
Introduction
In 1880, Charles Darwin, assisted by his son Francis, published their book
The power of movements in plants. In the last pages of the final chapter
the Darwins reflected on the sensitiveness of the tip of the radicle: “it is
hardly an exaggeration to say that the tip . . . acts like the brain of one of the
lower animals; the brain being seated within the anterior end of the body,
receiving impressions from the sense organs, and directing the several
movements” (Darwin 1880, p. 573). Charles Darwin was much taken with
the properties of the root tip. In his ‘Autobiography’ he records that he
“feltanespecialpleasureinshowinghowmanyandwhatadmirablywell
adapted movements the tip of the root possesses” (Darwin 1888a, p. 98).
The idea of a plant ‘brain’ surfaces again in a letter of 1880 from Darwin
to Sir Joseph Hooker in which he (Darwin) draws attention not only to his
new book but to the root tip in particular: “The case, however, of radicles
bendingafterexposureforanhourtogeotropism,withtheirtips(orbrains)
cut off is, I think, worth your reading . . .; it astounded me” (Darwin 1888b,
p. 334).
Communication in Plants
F. Baluška, S. Mancuso, D. Volkmann (Eds.)
© Springer-Verlag Berlin Heidelberg 2006