Other Functional Adaptations

Abstract

The subject matter of this book is multi-dimensionally related in so many different ways that it is difficult to accommodate it logically in a one-dimensional text representation that proceeds linearly. The organization of the subject material into chapters and sections has therefore been somewhat arbitrary. Frequent cross-references help to restore some of the multi-dimensionality. There are nevertheless topics which do not fit easily into the linear text sequence and so some of these have been gathered in this chapter under the heading, Other Functional Adaptations. The chapter has thus become rather a collection of odds and ends. Functional adaptation is a very attractive topic for botanists who are interested in xylem evolution, but it tempts many to walk on thin ice. Arber (1920) wrote: “One of the unfortunate results, which followed the publication of The Origin of the Species, was the acutely teleological turn thus given to the thoughts of biologists. On the theory that every existing organ and structure either has, or has had in the past, a special adaptive purpose and “survival value”, it readily becomes a recognized habit to draw deductions as to function from structure, without checking such deductions experimentally.” Too many structural features have more than a single function, and too many functions depend on several factors. Correlations become therefore easily unreliable and one begins to speculate wildly. However, there is more to it: random mutations may produce structural features that are functionally rather unimportant. It is rather futile to try to interpret such features for their adaptive value (van Steenis 1969; Baas 1976). Nevertheless, we must learn a great deal more about wood function before we can begin to speculate about adaptation. I suppose we are all entitled to a certain amount of speculation, although I normally prefer to reduce questions to basic simplicity, thus making them accessible to experimental tests. This chapter is the place where I have most often disregarded my principle.