SEED DEVELOPMENT IN BLACKBERRIES

Abstract

This study of blackberries deals with seed production and germination, describes the main steps in megagametophyte development of pseudogamous and syngamous varieties, and traces the development of both germinable and aborted seeds. Certain conclusions are drawn concerning the interdependence of maternal and filial tissues. The number of drupelets which develop in both pseudogamous and syngamous varieties depends, in part, on the pollen parent. A small but rather constant proportion of the drupelets display only a partial enlargement. Seeds of the well-developed drupelets are divided into three intergrading classes: (i) plump seeds, (ii) collapsed seeds, and (iii) an intermediate group. The general developmental features of the ovule and its contents are described. Regular megagametophyte formation is the rule in the syngamous varieties, but many irregularities, especially multiple gametophytes, are common in the pseudogamous species studied. Approximately a third of the seeds in the drupelets which appeared normal at 6 to 15 days after pollination did not contain an embryo. Some of the "eggs" were disintegrating, whereas others were still in a turgid condition. All the seeds which were imperfectly developed contained endosperm but only rarely was there an embryo or its remains. Reserve food was usually stored only in the chalazal region of the endosperm. The endosperm is believed to stimulate the transfer of nutrient materials to the seed. The embryo supplements this function as the seed approaches maturity, and influences the distribution of the storage products within the endosperm.