Division of the Generative Nucleus in Pines . 207 
the nuclear cavity before the spirem is established (Figs, 26 
and 29). Rarely, the nuclear membrane appears pushed in 
irregularly along its entire lower margin, as indicated in Figs. 25 
and 26 ; as a rule, however, there seems to be one deep, sharp 
indentation along one side of which the nuclear wall first 
gives way (Figs. 27 and 29). With the initial steps in the 
disappearance of the nuclear membrane the nucleolus is 
either not apparent or, if still demonstrable, it stains but 
feebly. When the membrane disappears along the entire 
lower portion of the nucleus, the kinoplasmic threads press 
so closely against it that it cannot be definitely demonstrated 
whether it passes into the cytoplasmic and the nuclear 
reticulum or becomes fibrous and contributes to the formation 
of the achromatic threads (Figs. 28 b and 29). The threads 
which have been packed so closely against the wall of the 
nucleus now press into the nuclear cavity and mingle with 
those which have entered from below; and the dense, granular, 
cytoplasmic area from which the threads diverge is gradually 
dissipated (Fig. 30). 
In the early stages of mitosis it is evident that there are 
present in the nuclear reticulum two kinds of granules, as 
described by Heidenhain (’93 and ’ 94 ). This becomes more 
apparent as the chromatin condenses to form the spirem. 
When the spirem is fully differentiated there is present in 
the nuclear cavity a loose, granular, achromatic reticulum. 
With the disappearance of the wall along the lower part of 
the nucleus this network seems to undergo a partial rearrange- 
ment. A portion of it is resolved into threads of more or 
less regularity, which in general assume a position parallel 
to the threads entering the nuclear cavity ; some of them 
become attached directly to the ends of these fibres, and 
doubtless contribute to their growth (Figs. 29-31). 
As the spindle-threads proceed in their development across 
the nucleus, the chromatic spirem collects in the region of the 
future nuclear plate, and becomes more or less massed to- 
gether, presenting an appearance somewhat comparable with 
that of synapsis ; at the same time it becomes homogeneous 
