An Embryological Study in the Rhododendron Subgenus Anthodendron Endl.

Abstract

1. Intraspecific and reciprocal pollinations were made with Rhododendron japonicum and R. mucronatum, and pistils were collected at established intervals after pollination. This material was sectioned and examined to observe rate of pollen-tube growth, fertilization, and subsequent seed development. 2. The azalea megagametophyte is typical of the Ericales. 3. Pollen-tube development is slow, and callose plugs occur frequently throughout the length of the tubes. Fertilization occurs about 96 hours after pollination under normal conditions. 4. In the development of the endosperm the primary endosperm nucleus gives rise to four free nuclei. These migrate and form a linear four-nucleate endosperm, and all subsequent divisions are followed by wall formation. This behavior differs from that hitherto reported by most workers who have described the Ericales as having an entirely cellular endosperm. 5. Inhibition of the pollen tubes in the style is a major barrier to intersectional hybridization but is not entirel...