Igto] YAMANOUCHI—CHROMOSOMES IN OSMUNDA 5 
chromosomes, separating at the equatorial plate, proceed to the poles 
and the vacuolation process follows, as already described. 
FORMATION OF CHROMOSOMES IN HETEROTYPIC MITOSIS 
The origin of the chromosomes in the spore mother cell is entirely 
different from that in vegetative mitosis. Some facts are well known 
and there is an immense literature based upon various material, 
but the extensive literature does not necessarily mean that all ques- 
tions have been settled; on the contrary, opinions and interpretations 
are still conflicting. 
Although the nucleus of a spore mother cell in the resting state 
does not appear very different from that of a vegetative cell, it has 
characteristic differences, such as its immense increase during the 
growth period, and the behavior of the chromatic substances outside 
the nucleus. The most important difference, however, is seen inside 
the nucleus, in connection with the origin of chromosomes. 
The chromatin network in the resting state, consisting of irregular 
ragged clumps and strands, at first begins to be transformed into 
more or less regular and less ragged strands, which are uniform in 
thickness for some distance. These strands are developed simulta- 
neously in various parts of the chromatin network, and at the very 
beginning of the transformation each chromatin thread thus formed 
has a thread running parallel to it; in other words, the threads come 
out of the network as two independent threads from the start. 
The pairs of threads at their first appearance are connected by 
fine fibrils, by means of which all these threads are connected into 
the single framework of the nucleus. As the delicate connecting 
fibrils become less and less conspicuous, the duality of the threads 
is shown with more clearness. The course of the threads being 
irregularly curved, it is hardly possible to determine their number 
at this time. The number is certainly less than the reduced number 
of chromosomes, and there may be only a single pair of threads. 
A close examination of the double threads or spirems in this 
Stage shows that they are not uniform in density or in thickness, but 
the chromatin material is distributed irregularly, so that the parts 
Where it is less densely aggregated stain lighter than the parts where 
it is denser (fig. 8). The knots in one of the double threads do not 
