The problems associated with the application of FT-IR to the characterization of coal structure are critically discussed. The controversies concerning band assignments are considered and it is concluded that the strong 1600 cm−1 band can be assigned to an aromatic ring stretching mode that in most coals is intensity enhanced by the presence of phenolic groups. The application of computer routines to the determination of OH and CH groups is considered. Established criteria for curve fitting are applied to the problem. Qualitative identification of functional groups is achieved, but consistent quantitative measurements will require a determination of the relationship between the extinction coefficients of resolved bands.

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The patterns of postmating reproductive isolation in general follow Haldane's rule that the heterogametic sex is much more likely to become inviable or sterile than the homogametic sex. There are two approaches to explaining the rule. The first approach assumes that genic divergence affects both sexes equally but their difference in chromosome constitution leads to the sex:dependent manifestation; for example, the heterogametic hybrids have a greater degree of X-autosome imbalance. The second approach assumes that genes affecting the heterogametic sex have evolved more rapidly and the genotypic difference between sexes is unimportant. Neither approach in its search for a unitary genetic basis of Haldane's rule has been successful. The major point of this article is that Haldane's rule is most likely a composite rule--the first approach is appropriate for hybrid inviability but is not sufficient for hybrid sterility, which requires the second approach in addition. Three lines of evidence are presented: (1) genes causing hybrid inviability generally do not behave in a sex-dependent manner and, thus, X-autosome imbalance is crucial; (2) interspecific crosses yielding sterility outnumber those yielding inviability by more than 10-fold in Drosophila and mammals; and (3) in Drosophila, genes causing hybrid male sterility greatly outnumber genes causing male inviability. Several models pertaining to the faster evolution of hybrid sterility in the heterogametic sex (than in the homogametic sex) are discussed. Finally, genes affecting the viability and fertility of interspecific hybrids seem to belong in a class distinct from those represented in mutagenic studies or those detected as intraspecific variations. The implications of this qualitative and quantitative break at the species level need to be heeded.

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SummaryFurther properties are derived for a class of invariant polynomials with several matrix arguments which extend the zonal polynomials. Generalized Laguerre polynomials are defined, and used to obtain expansions of the sum of independent noncentral Wishart matrices and an associated generalized regression coefficient matrix. The latter includes the /c-class estimator in econometrics.

The genetic analysis of reproductive isolation between species of Drosophila has now reached the resolution necessary to start answering one of the fundamental questions of evolution: what is the genetic basis of species differences? A.H. Sturtevant, one of the founders of Drosophila genetics, was fascinated by this question and thought he had found a way to analyse it when he realized that 'Drosophila melanogaster' was actually two species: D. melanogaster and D. simulans. By passing genes between these two species he hoped to investigate their genetic differences directly. No doubt he was disappointed to find that the D. melanogaster/D. simulans hybridization resulted only in unisexual sterile hybrids, a disappointment appreciated all the more by modern evolutionary biologists. Seventy-five years after Sturtevant's description of D. melanogaster/D. simulans hybrid sterility, we have discovered a strain of D. simulans that produces fertile female hybrids in crosses with D. melanogaster. Our discovery promises to bring the enormous resolution of D. melanogaster genetics to the study of reproductive isolation and species differences.

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