The two divisions of the spore mother cell in which the reduction takes place, follow each other very rapidly and are known as Heterotype and Homotype (Flemming), or according to the terminology of Farmer and Moore (1905) as the meiotic phase.
In the heterotype division the spirem thread is divided longitudinally before the segmentation occurs (fig.
Mottier, The Development of the Heterotype Chromosomes in Pollen Mother-cells, Ann.
Xxi.; On the Prophases of the Heterotype Mitosis in the Embryo-sac Mother-cell of Lilium, Ann.