Cytological Study of Oedogonium

1. Although the somatic mitosis of Oedogonium has already been shown by Strasburger and Wisselingh, O. grande shows the figures more distinctly than their illustrations, furnishing a complete series of the mitotic process, especially the behavior of chromosomes which show a remarkable resemblance to those of higher plants. This is due partly to modern methods of technique and partly to the species studied. 2. The number of chromosomes of this species is thirteen, an uneven number, in this respect agreeing with the uneven number nineteen in O. cyathigerum counted by Wisselingh. 3. In the spermatogenesis all important phases of the mitosis in the formation of both antheridia and sperms have been traced in O. grande. The most striking feature is found in the mitosis of the antheridial cell, in which the figure is oriented along the horizontal axis, while the cell division is to be transverse. But when the ring stretches, one of the daughter nuclei, which have been lying side by side, moves into the upper space and becomes separated by a cross wall. This seems to be an unusual condition in cell division and has never been described in Oedogonium. 4. The complete series of spermatogenesis of the dwarf male was found in O. nebraskense, which shows the formation of sperms very distinctly. 5. There are two types of oogenesis, one with a suffultory cell (O. nebraskense) and the other without (O. americanum). The behavior of the nucleus in oogenesis is different from that in the vegetative cell division, in staying in the same position or in migrating slightly toward the lower end of the cell, while the nucleus in the vegetative cell division migrates toward the upper end of the cell. Both show that they are the center of morphological and physiological activity. 6. As soon as fertilization takes place in O. americanum the spore coat develops from the fertilized egg. The spore coat consists of three layers: a thin and smooth outer one; a thick, half wavy and half smooth middle one; and a thin and smooth inner one. 7. In the formation of the zoospore, the behavior of the nucleus of the unknown species is a little different from that of O. tumidulum described by Strasburger, in not changing its position according to the various stages of the development of the zoospore. The nucleus of my material sinks just under the clear circle in which the cilia of the zoospore appear. The process of escape of the zoospore from the cell takes only a few minutes. Of the factors whic