Page:The yeasts (1920).djvu/35

 True transverse partition is met only with the Schizosaccharomyces of which we shall mention the principal species.

Sch. octosporus possesses round or oval cells; in young cells the oval form predominates. They elongate and, after having acquired a certain size, form a wall across the middle. This splits apart and the two cells become rounded. They elongate when they have achieved their growth, and finally separate completely; but often the two cells, though remaining attached, undergo a new partition which makes two daughter cells. Thus a row of cells is secured which are arranged parallel to each other. Sometimes, when multiplication is very rapid, a primary transverse wall is formed which makes two cells; without separating, these produce another partition. In this manner, small filaments may be found which eventually break apart.

At the end of some culture periods and also under certain conditions the cells show a tendency to take spherical forms. In this case partition is accomplished in the same manner; but it also often happens that, on account of rapid multiplication, the two cells set apart by a partition remain attached without rounding their adjacent planes. Each may then form transverse partitions which form two new cells. Such an arrangement resembles the sarcina grouping. In this latter case partition is accomplished in two directions.

The daughter cells remain associated for some time, giving the appearance of colonies. These colonies present different appearances, depending upon the age of the culture. In the early stages of their development these colonies are composed of elongated cells. Later muriform cells are apparent.

In the other Schizosaccharomyces (Sch. Pombe and Sch. mellacei), in which the cells look like drum sticks, division is accomplished in the same manner. When they have acquired their maximum size, the cells form a partition, which divides them into two cells. They either separate immediately or remain attached for some time.