Background: The
English plant morphologist Agnes Arber was both a skilled
interpreter of the plant world, and a critical observer
of the relationship between vision and the mind's act of
interpretation. She wrote many botanical works, including
a history of Herbals (1912) and meticulous and beautifully
illustrated books on water plants (1920), monocots (1925),
and grasses (1934). "The Natural Philosophy of Plant
Form", written towards the end of her career, is both
a distillation of her extensive botanical knowledge and
a bold attempt to integrate all aspects of plant morphology
into a single coherent theory. In it, Arber side-steps
the historical dichotomy between "leafness" and "stemness" by
visualizing the plant as a collection of shoots, and by
highlighting the underlying correspondences between stem
and leaf. In particular, she proposed that a leaf should
be thought of as a partial shoot, arising laterally from
its parent whole shoot, and cites as evidence both the
many cases of leaves that have elements of the radiality
and extended growth of stems, as well as the branched nature
of compound leaves and of the venation in simple leaves.
A leaf is a partial shoot because it usually only repeats
some of the characters of the whole shoot, having limited
apical growth, accompanied by lateral growth that results
in dorsoventrality. This is interesting from an evolutionary
developmental genetic viewpoint, because it has been shown
that genes such as phantastica are necessary both
for lateral growth as well as for dorsoventral identity
of the leaf (Waites and Hudson, 1995). If phantastica is
knocked out, a much more stem-like organ is produced (Kim
et al., 2003). Modern genetics thus confirms the connection
between leaf and stem, but might go further to say that
a stem is but a partial leaf!
Arber's
lasting contribution is her critical insight into the deep
developmental and logical relationships between stem and
leaf, and her novel interpretation of the plant as a collection
of shoots in various degrees of wholeness. Her philosophical
approach to plant morphology may also provide new ways
of relating morphology to its underlying genetic and developmental
causes.
Agnes
R. Arber. 1912. Herbals, Their Origin and Evolution, A
Chapter in the History of Botany, 1470-1670. Cambridge
University Press, Cambridge. 253 pages. volume
at Cambridge University Press
Agnes
R. Arber. 1920. Water Plants: a Study of Aquatic Angiosperms.
Cambridge University Press, Cambridge. 436 pages.
Agnes
R. Arber. 1925. Monocotyledons: A Morphological Study.
Cambridge University Press, Cambridge. 258 pages.
Agnes
R. Arber. 1934. The Gramineae: a Study of Cereal, Bamboo
and Grass. Cambridge University Press, Cambridge. 502 pages. volume
online at Cornell (searchable
text and scanned pages available from that link)
Minsung
Kim, Sheila McCormick, Marja Timmermans, and Neelima
R. Sinha. 2003. The expression domain of PHANTASTICA determines
leaflet placement in compound leaves. Nature 424(6947):
438-443. first
page | full
text article | article
in pdf format
Richard
Waites, and Andrew Hudson. 1995. phantastica:
a gene required for dorsoventrality of leaves in Antirrhinum
majus. Development 121(7): 2143-2154. abstract | article
in pdf format
submitted
by: Andrew
Doust
