The nucleus remaitis for some time at the base of the ascus, where
the latter narrows to form the short stalk; but as it passes on in tts
development toward the formation of the chromosomes and the spindle,
it generally migrates to a region higher up and nearer the middle of the
enlarged portion of the ascus. The further differentiation of the chro-
mosomes now continues. The process seems to be as follows : A more
densely staining portion of each thread becomes differentiated at some
point in its length, forming an elongated and bent rod-shaped body,
which is to become the chromosome. The process of differentiation
seems to consist in the drawing together and Uic aggregation at some
point of the more densely staining constitu tents of the strand. At the
same time a contraction or shortening of the whole thread occurs. The
segregation of the more stainable portions of the thread into the chro-
mosomcs leaves an achromatic filament or bundle of fibrill<T connecting



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.
