Comparative Experiments as a Key to the Ecology of Flowering Plants

The rationale behind two methods of explaining the present distribution of flowering plants is examined. Reasons are put forward to explain why spatial correlation between plant density or vigor and environmental variation does not usually lead to an understanding of mechanism or adequately prepare the way for experimental work. Observations based on the concepts of A. S. Watt are more useful in that they define events critical in the establishment or maintenance of pattern; events in the field, rather than correlations, are the proper subjects to be elucidated by experiment. An alternative starting point for investigations is the comparative experiment in which one seeks to recognize unusual features characteristic of plants from the same habitat. Among these features "susceptibilities" are of greatest interest. A means of extrapolation of laboratory results to the field is clear if we recognize that pronounced susceptibilities arise as an indirect consequence of adaptations. Hence we may regard these phenomena as a valuable clue to the factors of selective importance in the past or present habitats of the species or genotypes concerned.