SPECIAL NUCLEAR PHENOMENA. 45 



now Stain more deeply than in the prophase stages and appear blue or 

 violet in the triple stain. 



In describing and figuring the three successive divisions of the 

 nucleus of the ascus I have had a great abundance of figures at my 

 disposal and have chosen to select those stages in each division which 

 mutually supplement each other rather than to give a full series of 

 stages in any one division. In this way the evidence that the number 

 of chromosomes is the same throughout and that the central bodies are 

 present at each stage is brought out more clearly. 



If we compare the chromosomes in the equatorial plate with the 

 spirem strands in the prophases we get evidence of a great reduction 

 in volume. This may, of course, be partially due to condensation of 

 their substance, although in reality the spirem strands (figs. 48, 49) 

 appear quite as dense as do the chromosomes in the equatorial plate. 

 However, as we have seen, the formation of the chromosome from a 

 strand of the spirem consists in the segregation of two substances pres- 

 ent in the spirem. The densely staining chromatin aggregates in the 

 chromosomes, leaving the achromatic portion as a series of threads 

 connecting the chromosomes to the central body, and these threads later 

 form the spindle. 



Following the equatorial plate stage, the chromosomes are drawn 

 back to the spindle poles, and during this process again their number 

 may be easily determined. Fig. 54 shows an early metaphase in which 

 the daughter chromosomes are beginning to separate. In fig. 55 it is 

 perfectly plain that sixteen daughter chromosomes are being drawn back 

 to the poles, eight on each half of the spindle. These figures are abun- 

 dant in the mildews and are very easily fixed and stained. Maire has 

 evidently seen more than four chromosomes in many cases in the 

 prophases, but maintains his contention by calling these more numerous 

 bodies " prochromosomes " and asserting that they later fuse into four 

 true chromosomes. He will hardly maintain, however, that the bodies 

 shown on the spindle in fig. 55 are prochromosomes, and there can be 

 no question that there are at least eight of them on each half of the 

 spindle. With poor fixation it is possible to find the chromosomes of 

 the mildew fused together into irregular masses, as may happen also in 

 the pollen mother cells of the larch or lily, and it is doubtless such cases 

 of poor fixation which have misled Maire and Dangeard. The polar 

 asters at these stages are very strongly developed, and it is apparent 

 that some of the astral rays extend to the plasma membrane of the ascus. 



The central spindle fibers left after the chromosomes have reached 

 the poles seem to disintegrate and pass over into the general cytoplasmic 



