SPECIAL NUCLEAR PHENOMENA. 47 



reticulum is for any reason drawn together and away from the nuclear 

 membrane. In such cases the chromatin threads are always attached 

 to the center, though they may be drawn away from the membrane 

 everywhere else. This condition is also conspicuous in the figures of 

 Erysiphe which I have already published. The polar asters through 

 these stages are very sharply differentiated, the fibers extending in 

 some cases almost, if not entirely, to the plasma membrane of the ascus 

 (figs. 55-61). 



The daughter nuclei formed by the division of the primary nucleus 

 of the ascus, as just described, never grow to the size of the mother 

 nucleus. Their volume is apparently not more than one-half that of 

 the primary nucleus. As a rule they divide again immediately, though 

 in some cases apparently a considerable period may intervene. 



Fig. 62 shows an early stage of the spirem of the nucleus in the 

 binucleated stage of the ascus ; and fig. 63 a, b shows a stage in the sepa- 

 ration of the daughter centers and the formation of the spindle. The 

 chromosomes appear as oblong, densely stained, bent or irregular bodies 

 in a fairly dense group in the antipolar region. The group was cut in 

 two in sectioning and is reproduced in the two figures (63^ b}. The 

 halves of the spindle appear as broad series of fine achromatic fibers 

 and the centers have their characteristic flat, disk-shaped form. The 

 stage is a little earlier than that shown in fig. 52 for the first division. 

 It differs in that the nuclear membrane is in this case still partially 

 present, though breaking down in certain portions. Fig. 64 shows a 

 somewhat later stage, in which the centers are farther apart and the 

 halves of the spindle diverge at a correspondingly greater angle. In 

 this case the polar asters appear as well-developed systems of fibers 

 radiating from the central bodies into the cytoplasm. 



Fig. 65 shows the two nuclei of the ascus in the equatorial plate 

 stage. The upper spindle lies in the plane of the section and the lower 

 is cut through obliquely, so that only one pole and one half of the spindle 

 appear in the section. As is to be seen, eight chromosomes are present 

 at this stage also. In Phyllactinia, as in all the Ascomycetes I have 

 studied, the number of chromosomes remains the same through all three 

 divisions of the primary nucleus of the ascus. Fig. 66 shows a further 

 stage in the division of the two nuclei. One spindle lies in the long 

 axis of the ascus and the other almost transversely and in the upper end 

 of the ascus. As a rule only two spores are formed in the ascus of 

 Phyllactinia; and a study of the further stages shows that both the 

 daughter nuclei produced from this transverse spindle will remain in 

 the upper end of the ascus and fail to become centers for spore forma- 



