Microsporogenesis and Embryogeny in Certain Species of Bromus

Abstract

1. Bromus marginatus and B. rubens are octoploid and tetraploid respectively; B. villosus is variable between octoploid and decaploid. 2. Polyploidy and other irregularities in the maturation division indicate that these species may be hybrids. 3. Lagging bivalents are found in B. villosus and B. marginatus. An irregular homeotypic division, showing much lagging and extrusion, occurs in B. villosus. 4. Varying types of chromatin extrusion are found in all three species, together with polycary and sterile pollen. 5. No examples of cytomyxis were observed. 6. Megasporogenesis and embryo sac development appear to be rather typical for the Gramineae. 7. Antipodals generally vary in number from five to eight, with a maximum of ten seen in one instance. Their nuclei are large, are often organized into cells, and finally occupy a lateral position just below the center of the sac, in which position they undergo dissolution, after an existence considerably longer than that characteristic of smaller cells.