Abstract
woody, as he (1962, 1980) maintains. States of characters may be primitive: suites of characters, that is individual organisms, are widely, but not universally, held to be acted on by natural selection. In an elegant series of papers, Harper and his co-workers (see Burdon, 1980) have made an extremely convincing case for there being very high levels of selection within plant species, yet it can be cogently argued in a zoological context, as it has long been in a botanical one (e.g Arber, 1920, p. 131), that any particular character-state may be in no way 'adaptive' (Gould and Lewontin, 1979). In an important review of the evolutionary polarity of character-states, Stevens (1980) has drawn attention to the apparently repeated trends of morphological variation within large genera and families of angiosperms. Such trends are listed by Ehrendorfer (1973) and have been discussed by Corner (1967). An example in overall morphology or plant architecture is provided by the survey of trees in the work of Halle, Oldeman and Tomlinson (1978), where, within families of angiosperms, the same 'models' of construction have been achieved again and again, that is, at least some of these models represent grades of organization. Using currently held views of evolution, it can be argued that the earliest angiosperms must have possessed a suite of characters which suited them to the Cretaceous environment apparently dominated by ferns and gymnosperms: the elucidation of that suite has been the goal of those who seek the possible ancestors from scrutiny of the known fossils (Takhtajan, 1969) or hypothesize from the correlations of character states in those modern angiosperms which seem to be evolving rapidly (Stebbins, 1974). Apparently very reasonably, it has been argued that the answer will only be found in the fossil record (Hughes, 1974) and a reconsideration of the Cretaceous fossil record (see Doyle, 1978) has led to the recognition of pollen and leaf character-states now typical of the groups of
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