The Floral Morphology of Clethra alnifolia with some Notes on C. acuminata and C. arborea. Contributions from the Hull Botanical Laboratory 632

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Abstract
Descr. of the organography, floral development, vascular anatomy of the flower, anatomy of the floral organs, microsporogenesis, and megasporogenesis in C. alnifolia. and notes on the organography, vascular anatomy, and anatomy of the floral organs in C. acuminata and C. arborea are presented. A comparison of the characteristics of the Clethraceae, as exemplified by the 3 species studied, with those of other groups in the Ericales is made in order to elucidate as much as possible the relationships within the order. The Clethraceae, in common with most of the Ericales, are pentacyclic, pentamerous in most floral whorls, actinomorphic, hypogynous, and hermaphroditic. Characteristics peculiar to the family are a fully developed endothecium in the anther and a 3-branched style. Other features found in the Clethraceae and in only a few other spp. in the Ericales are choripetaly, absence of a disk, "stellate" pubescence, extrorse position of the anthers during development, single pollen grains, and a tricarpellate ovary. The pattern of microsporogenesis is similar to that found in most angiosperms, and megagametophyte development follows the Normal- (Polygonum-) type. Compared with other groups in the Ericales, the family is not so primitive with respect to the vascular anatomy of the flower as it is with respect to certain of its other morph. features such as the presence of a true well developed endothecium in the anther, the absence of a disk, and the fact that each carpel is represented by a separate branch of the style and stigma.