149 
Meiotic Mitoses of Osmunda. 
coalescence of the approximated threads has occurred, and there is consider- 
able thickening of the spireme filament. The nucleus has been cut some- 
what superficially, but the preparation for conjunction is manifested both in 
the looping over and drawing together of the sides of the loops, and in the 
fine connecting transverse strands. 
The stage when the univalent spireme (filament) is uniformly spread 
throughout the nuclear cavity appears to be of short duration, for almost 
immediately it tends to aggregate preparatory for second contraction 
(Fig. 60), and at the same time becomes stretched and smoother in outline. 
It now shows various degrees in the process of conjunction in pairs; some 
lengths may be merely running parallel, whilst others, though still separate, 
are joined at intervals by fine strands (Fig. 59) ; others form a closed ring 
(Fig. 61) ; others are twisted over one another (Fig. 61) ; whilst others are 
closely conjoined side by side for some distance (Fig. 60) and then diverge. 
If each nucleus in a sporangium at this stage be examined, it will be found 
that the spiremes in the majority show some signs of conjunction. Fission 
is still occasionally visible as in the loop of Fig. 62. Moreover, there may 
be a straightening out of the loops and also beautiful anastomosis, but as 
these figures are somewhat aberrant they have not been published. 
The massing of the spireme filaments preparatory for second contrac- 
tion increases (Fig. 62), and at the same time they withdraw from the 
periphery of the nucleus and definitely become transversely segmented 
(Figs. 62 and 63). Conjunction meanwhile proceeds (Fig. 63). Nuclei cut 
superficially show segments of conjoining spireme filaments (PL X, Figs. 
6 4, 65, and 66) which bear a striking resemblance to the future completely 
organized heterotype chromosomes (PI. XI, Figs. 80 and 81) except for 
their slightness as compared to the concentrated mature segments. 
It may here be emphasized that the breadth of the spireme filament 
affords no criterion whatsoever on which to build any calculation as to the 
stage reached, except in the extreme case mentioned above, and also in the 
pre- and post-synaptic spiremes before and after association. Thin spireme 
is so often due solely to tension, as in associating half univalent spiremes 
(threads) and conjoining univalent segments (filaments), and directly the 
strain is relaxed the spiremes shorten and thicken. 
Fission is apparent in the free portions of univalent sides (filaments) of 
several of these chromosome-like combinations (Figs. 64, 65, and 66). Con- 
junction of the univalents (filaments) becomes increasingly close. Figs. 67, 
68, and 69 have all been taken from the same sporangium, and Figs. 67 and 
69 from the same microscopic field. In Fig. 67 comparatively little conjunc- 
tion has taken place, whilst in Figs. 68 and 69 conjunction is advanced. 
Lawson ( 14 ) has published two identical stages in Smilacina ( PL I, Figs. 15 
and 16). He states that the large number of threads 1 present in his Fig. 15 
1 ‘ Filaments according to the nomenclature adopted in this paper. 
