﻿238 BOTANICAL GAZETTE [april 



perhaps two large vacuoles in the center, and occasionally smaller 

 ones near the edge {figs, 10, 11). The protoplasm then lies as a 

 thick peripheral zone, and the nuclei {fig- 5) are distributed at 

 varying distances between the oogonial wall and the boundary of 

 the vacuole. 



This is the period when one may expect to find the nuclei in 

 mitosis. This event happens to most nuclei at about the same 

 time, and good preparations of this stage of oogenesis are very 

 striking [fig, 5). The oogonium is filled with the diamond- 

 shaped spindles inclosed in nuclear membranes. Three stages 

 of mitosis are shown in figs, J-Q. It will be noted that the 

 spindle is intranuclear. Fig. 7 presents the condition just pre- 

 vious to metaphase, with the chromosomes, four in number, at the 

 nuclear plate and the nucleolus lying outside of the spindle. 

 Fig, 8 is of a stage shortly after metaphase, when the two sets 

 of daughter chromosomes have separated and are about to pass 

 to the poles ; the nucleolus is still present, but smaller and stain- 

 ing faintly. Fig, p is of anaphase, the two groups of daughter 

 chromosomes, four in each, lying at the poles of the spindle and 

 the nuclear membrane manifestly about to disappear. The 

 nucleolus probably dissolves ; at least I have never been able to 

 follow it much beyond metaphase, but surviving it would of 

 course soon be lost in the granular cytoplasm after the breaking 

 down of the nuclear membrane. Although granules are some- 

 times present at the poles of the spindles, the latter are generally 

 entirely free from appearances that might suggest centrosomes. 

 It will be noted that this description of mitosis in Saproleg- 

 nia is similar in all essentials to the accounts of Wager (1896), 

 Stevens (1899, 1901), and myself (1900) for Albugo; Wager 

 (1900) for Peronospora; Miyake (1901) and Trow (1901) for 

 Pythium; and Stevens ( 1902) for Sclerospora. The studies 

 cover a wide range of forms and material. They agree in describ- 

 ing the spindle as alwa^^s intranuclear and without centrosomes. 

 The nucleolus is a structure always distinct from chromatic 

 material and always, so far as we know, disappearing during 

 mitosis by dissolution or extrusion into the cytoplasm. The 

 chromosomes are derived from a linin network, and after mitosis 



