20 SEED COAT ANATOMY AND TAXONOMY IN EUCALYPTUS. By E. Gaura and L. D. Pryor. (Plate i; nineteen Text-figures.) [Read 26th March, 1958.] Synopsis. Anatomical and histochemical investigations of the seed coat of Blakely's two Renantherous Sections of Eucalyptus aimed at revising these groups show for the bulk of the species a remarkable consistency. The seed develops from an anatropous, bitegmic, crassi-nucellate ovule. The salient testa characters are : the outer integument is several layered, with its outer epidermis built up by sclereids, its inner epidermis crystal-bearing but without forming a typical "crystal epithelium" ; the inner integument persistent, two-layered and suberized. An elaborately ramified vascular system extends from the basal hilum to the distal chalaza. However, three of Blakely's series, Ochroxylon, Steatoxylon and Myrtiformes, deviate considerably from each of these testa features and vascularization pattern and probably are not correctly placed in the Renantherae. Introduction. Since Bentham's (1866) original treatment the taxonomy of Eucalyptus has been based on various characters of the anther, such as shape, mode of dehiscence, attachment to the filament and relative position of the gland. It has been obvious more recently that some of the groups formed on this basis are not homogeneous. It has now been found that the anatomy of the seed coat, together with some morphological ovule and seed characters, promises to give valuable data for a regrouping of some species. The value of the study of seed coat anatomy is not confined to its application to taxonomy, since it is likely also that seed coat structure and seed behaviour are related. Blakely's "Key to the Eucalypts" is the most recent classification of the genus, and undoubtedly the most satisfactory yet published. In such a large genus, however, it is to be expected that even in so excellent a work there will be anomalies in the arrangement of some of the species, and at different times some of these have been suggested by investigations carried out in other ways. For example, Blake (1953) has shown on general morphological grounds how the species belonging to the Clavigerae as understood by him form a natural group, but in Blakely's "Key" they are partly separated. It has also been suggested (on the grounds of cotyledon shape) that some species having bisected cotyledons and separated by Blakely in his "Key" would more appropriately be placed together in the same taxon (Pryor, 1956). Amongst all of Blakely's groups, however, the combined group Renantherae and Renantherae-Normales, containing about 100 species, is one which possesses a high degree of homogeneity, and it seems clear that this group, largely as defined by Blakely, might well be. constituted a subgenus. It was already known at the time this investigation began that in morphological characters the seed of the great majority of species within this composite group had features in common but at the same time these were to be seen seldom in species placed by Blakely in other sections. It seemed likely, therefore, that this group would be essentially a natural unit. It followed, therefore, that if a similar uniformity were found in seed coat anatomy this would conform with this view. Further, if among the species thus placed together by Blakely occasional exceptions to the common pattern of seed coat structure were found, it might be deduced that these were incorrectly included in the group. At this point, therefore, it appeared that an examination of seed coat structure would be profitable and the study was commenced. Proceedings of the Linnean Society of New South Wates, 1958, Vol. lxxxiii, Part 1.