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APOMIXIS WAS FOUND in northeastern American polyploid blackberries during the course of breeding experiments conducted by Einset (1951). Twenty-four species and clonal varieties of blackberries (subgenus Eubatus, basic chromosome number 7) with somatic chromosome numbers ranging from 21 to 63 were selfed, open-pollinated, or crossed with a blackberry plant having a different chromosome number. Pollination was essential for seed set in every case. IChromosome counts showed that 80100 per cent of the seedlings of 21-, 35-, 49or 63chromosome seed parents possessed the same chromosome number as the female parent, whether it had been selfor open-pollinated or crossed with a male parent of a different chromosome number. When 28-chromosome seed parents were crossed with odd-ploid pollen parents 80 per cent of the seedlings were tetraploid. These seedlings were assumed to have developed from unfertilized, unreduced eggs. Seedlings having more than the somatic chromosome number of the female parent made up 0-7 per cent of the total progenies of the seed parents of each level of ploidy. Most of these were considered to have arisen from fertilized, unreduced eggs. Twenty-eight-chromosome seed parents produced 14-chromosome offspring totalling 6.3 per cent of the progenies, indicating that a reduced egg could develop parthenogenetically. Many aneuploid seedlings of polyploid seed parents conceivably originated from the union of reduced eggs and sperm, one or both having an aneuploid chromosome number. Seedlings resulting from the development of fertilized reduced eggs undoubtedly composed part of the tetraploid progeny of open-pollinated 28-chromosome seed parents, but could not be detected by somatic chromosome counts. The present paper will describe the development of the embryo sac in a diploid species of blackberry which reproduced sexually (Einset, unpublished data) and in six polyploid species which behaved pseudogamously (Einset, 1951). The terminology used will be that of Maheshwari (1950). MATERIALS AND METHODS.-Embryological material was collected from Rubus allegheniensis Porter (2x), R. canadensis L. (3x), R. localis Bailey (3x), R. beltobatus Bailey (Kittatinny) (4x), R. abactus Bailey (5x), R. meracus Bailey (7x), and R. flagellaris Willd. (9x). Rubus allegheniensis was growing wild in a hedgerow in Geneva, N. Y. The rest of the material was gathered from either the same plants or vegetative propagations of the same plants in the collections of the New York State