SPECIAL NUCLEAR PHENOMENA. 43 



the chromosome to the pole. The process is analogous to the short- 

 ening of the chromatin thread, which is common in the higher plant 

 and animal cells in the prophases, but differs from it in the fact that the 

 chromosomes are throughout the process so conspicuously attached to 

 the pole. It is generally agreed that the chromatin thread in the higher 

 plants consists of two substances; but the conspicuous separation of 

 these two constituents during the shortening of the chromatin thread 

 seems to be peculiar to the mildew. Still it is to be remembered also 

 that there is in many cases for example, in the pollen mother cells of 

 the larch at about this stage a large increase of linin fibrils in the 

 nuclear cavity, and it is at least possible that these fibrils arise from the 

 spirem thread in the process of the differentiation of the chromosomes. 

 The chromosomes appear now as oblong or irregular bodies connected 

 to the central body by fine pale-blue stained or grayish fibers. They 

 are distributed irregularly in the nuclear cavity, and in a polar view of 

 the nucleus may appear as if supported in an anastomosing reticulum. 

 They may be pressed closely against the nuclear membrane in some 

 cases, and in others they may lie in the central region of the nuclear 

 cavity or may be closely pressed against the nucleole. 



The spindle is formed in Phyllactinia essentially as I have described 

 for Erysiphe (38). The central body divides and the daughter centers 

 migrate away from each other on the surface of the nuclear membrane. 

 In Erysiphe and many Discomycetes the nuclear membrane remains 

 intact till the diaster stage. In Phyllactinia, at least in some cases, it 

 may disappear much earlier. The separation of the daughter centers 

 divides the achromatic filaments which connect the chromosomes to the 

 central body into two cones or bundles. This process seems also to 

 bring the chromosomes farther and farther into the antipolar region 

 of the nucleus, where they form a rather dense group connected by 

 broad bundles of fibers with the daughter centers (fig. 52) . The bundles 

 or cones of fibers are distinct until near their antipolar ends, where they 

 cross and interlace in connecting with the chromosomes. 



This figure resembles that of Hermann (43, Taf. 31, figs. 8-9), in 

 which the mantle fibers extend from the spindle poles toward the chro- 

 mosomes. There is, however, this essential difference, that according 

 to Hermann the mantle fibers are at this stage for the first time extend- 

 ing toward and becoming connected with the chromosomes, while (as 

 we have seen in the ascus) the chromosomes have been continuously 

 attached to the centers through all the preceding stages of nuclear devel- 

 opment. Whether there is longitudinal splitting of the individual fibers, 

 or whether they are merely separated into two groups, I have been 



