. Contributions from the Botanical Laboratory, vol. 4. Botany; Botany. 244 PENNYPACKER-ON THE BEACH PLUM A STUDY IN PLANT VARIATION 245 anthers are two lobed and bear numerous triangular-shaped pollen grains. The flowers are apparently proterogynous, since the stigma matures before the flower is fully open and may easily be seen protruding between the petals of a partly opened flower bud, but homogamy is probably not uncommon. The style projects in the middle of the flower beyond the obliquely diverging stamens, and is 10 to 20 mm. long. The ovary is one celled and characterized by two pendulo
. Contributions from the Botanical Laboratory, vol. 4. Botany; Botany. 244 PENNYPACKER-ON THE BEACH PLUM A STUDY IN PLANT VARIATION 245 anthers are two lobed and bear numerous triangular-shaped pollen grains. The flowers are apparently proterogynous, since the stigma matures before the flower is fully open and may easily be seen protruding between the petals of a partly opened flower bud, but homogamy is probably not uncommon. The style projects in the middle of the flower beyond the obliquely diverging stamens, and is 10 to 20 mm. long. The ovary is one celled and characterized by two pendulous ovules. Frequently the flowers are andro-dioecious which would account for the profusely abundant blooms matured on every bush during April and May, and also for the total lack of fruits on some bushes, the rarity on others, and the extreme abundance on still others. The last noted would naturally be those that developed stamens and a well formed pistil with swollen ovary and elongated style. At Hainesport, N. J. the writer has observed bushes for three years, during which time they have never set fruit, yet have constantly bloomed in great profusion. The same condition pre- vails in other localities. The flowers are insect pollinated as is indicated by the vast horde of Hymenoptera which frequent them during the warm part of the day. The showy white corolla and the nectary are the chief attractions for insects as the flowers are practically odorless. Cross pollination is favored by most writers, and such a view seems likely from the fact that the bee in order to obtain the nectar must get far into the interior of the flower. In so doing it seems hardly possible for it to miss touching the stigma. Knuth states that automatic self-poUination appears regularly to take place in hermaphroditic flowers of the Pruneae should insect visits fail. Whether this is effective or not seems doubtful, as Kirchner states that numerous bushes observed by him rarely set fruit. The true ex- pl
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