Introduction: modules and architecture

The shape of the canopy influences many important aspects of the growth and development of plants and such effects are felt at many levels. Differences in canopy form may affect not only how much photosynthetically active radiation is intercepted by plants but may also regulate the spectral composition of radiation that filters to lower levels in the canopy and thus have photomorphogenetic consequences. The extent of shading both by and from close neighbours will also be affected by canopy shape, as will the degree of presentation to, or concealment from, consumers of nutritious foods such as fruits, leaves and buds. In a more agricultural context, canopy arrangement influences the extent to which disease spores or the droplets of a chemical designed to kill them (or prevent their development) can enter infectable zones.

The above ecological repertoire of plants is linked directly to their gross form and invites an obvious question concerning their evolution, namely: does the architectural ‘type’ of a plant have a rôle in the (Darwinian) fitness of an individual or, in other words, have certain whole plant forms been selected during evolution while others have been less successful?

This question forms the major theme of this chapter although Fisher (1984) has recently considered a similar topic. In addition, in order to better understand the mechanisms behind the magnificent variability in plant form that we see, some recent experimental data indicating the rôle of genomic changes in determining plant shape will be presented.