Studies of Floral Morphology in the Ericales. II. Megasporogenesis and Megagametophyte Development in the Andromedeae. Contributions from the Hull Botanical Laboratory 634

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Abstract
The mature ovules of 22 spp. of the Andromedeae and fairly complete development of the megagametophyte of 15 of these (Andromeda glaucophylla, A. polifolia, Cassiope mer-tensiana, Chamaedaphne calyculata, Enkianthus cernuus, Epigaea repens, Leucothoe axillaris, L. catesbaei, L. recurva, Lyonia ligustriria, L. mariana, Neopieris nitida, Oxydendrum arboreum, Pieris floribunda, and Xolisma fruticosa) are described. Certain features are characteristic of the ovules of all spp.: single integument, single-layered evanescent nucellus, archesporium of a single cell which gives rise directly to the megaspore mother cell, the cells of the outer layer of the integument containing a tannin-like substance, the inner layer of the integument more or less differentiated as an endothelium in the region of the nucellus, the ovules anatropous to campylotropous, and the penetration of the micropyle by the megagametophyte after disintegration of the nucellus. With the exception of one sp., a single developmental type is found for all spp. studied in detail: Polygonum Type. The tetrad is linear, and the 3 micropylar spores normally disintegrate, leaving the chalazal one to function. Development in Cassiope mertensiana usually corresponds to a modified Allium Type. No walls are formed during meiosis. Usually a single wall develops during the tetrad stage, separating 2 nuclei from 2. One 2-nucleate cell disintegrates, and the other functions as the 2-nucleate gametophyte. Wall formation and disintegration in the tetrad are variable, and an essentially Polygonum -Type development is occasionally found. Variation occurs in ovule size, number of layers in the integument, size and fate of the antipodals, shape of the synergids, time of fusion of the polar nuclei, degree of bulging of the micropylar end of the mature gametophyte, and extent of bending of the ovule and gametophyte toward the campylotropous condition. Ovule and megagametophyte characteristics in the Andromedeae correspond to those of the others of the Ericales that have been described, except for the Allium-Type development in C. mertensiana. Variations in ovule characteristics within the Andromedeae show considerable agreement with the affinities tentatively suggested in an earlier paper based on the vascular anatomy and organography of the flowers.