J 57 
Meiotic Mitoses of Osmunda. 
may be confused. A well-defined phase, taken without its context, may be 
misleading and give rise to an error of judgement. For example, the parallel 
threads of the heterotype prophases may be exceedingly striking and 
definite, but it is impossible to offer a fully reasoned statement as to their 
homology, if an interkinetal rest exists between the last premeiotic division 
and the heterotype prophase during which all visible continuity is lost. Or 
again, fission in the post-synaptic spireme may be very evident, but this 
stage may be succeeded by most confused hollow spireme and second con- 
traction phases, thus obscuring the conjunction of univalents. This has led 
to the very commonly expressed inference that the disjunction of univalents 
after second contraction is the opening out of the fission observed in 
the substance of the post-synaptic spireme. 
It is believed that no conclusion can be drawn from the study of 
a series of nuclear phases of any one particular animal or plant. In order 
to expand this suggestion, it is proposed to compare the critical stages of 
the heterotype division in four plants, Galtonia (3), Primula (4), Crepis (5), 
and Osmunda . Each exhibits not only individually distinctive characters 
which dominate its mitoses, but shows considerable variation in the details. 
The most instructive point in Galtonia is the direct passing of the 
telophase of the last premeiotic division into the meiotic prophase with no 
intermediate rest ; consequently the origin of the parallel threads of the 
heterotype prophases can be traced directly to the longitudinally split 
chromosomes of the preceding telophase. This fact substantiates the nature 
of each thread of the parallel pair as representing the longitudinal half of 
a somatic chromosome. None of the other three plants show this all- 
important character so clearly. In Osmunda the homology can occasionally 
be traced, but not in so indubitable a manner, and a rest may intervene 
between the two divisions. In Crepis and Primula there is invariably 
a complete rest during which all visible chromosome continuity is lost. 
To proceed to synapsis. This stage is only really clear in Osmunda , 
on account of the distinct individuality maintained as between the threads. 
Under favourable conditions, many of the parallel threads of presynapsis 
can be seen, in a single nucleus, to be simultaneously in the act of closely 
associating in pairs. The contrast between the fine associating threads 
going into synapsis and the resultant thick emerging spireme filament is 
exceedingly striking. In Galtonia , Primida , and Crepis , the density of the 
synaptic knot obscures the course of events there taking place. 
To pass on to the complex stages between hollow spireme and early 
diakinesis. Primula shows the conjunction of filaments in pairs, i. e. of 
portions of univalent spireme, most clearly and diagrammatically. The 
figures are exceedingly sharply defined, and the univalent spireme filament 
is homogeneous, showing no fission, which simplifies the following out of 
the process. Moreover, in two species, P. floribunda and P. kewensis 
