555 
in Pinus and Thuja. 
Fig. 4. A cell from the same loculus as above. Many of the linin strands have been drawn in. 
The chromomeres have become somewhat evenly distributed along the linin strands and an incom- 
plete spirem is present. Some of the chromomeres still show clearly at this time. No indication of 
fusion or conjugation of chromomeres or threads. The cells are still in tissue connexion. 
Fig. 5. Pinus austriaca. Complete synapsis. The cell has rounded up and the nuclear com 
tent is in the tightly contracted condition. Nothing intelligible can be seen at this time. 
Fig. 6. From the same loculus as Fig. 5. The synaptic mass is beginning to loosen. Loops 
project out from the dense mass into the cavity. The chromomeres have assumed a striking uniformity 
in size and form. The thread is clearly double and the chromomeres occur quite uniformly 
in pairs. 
Fig. 7. Tangential view, same stage as Fig. 6. The double nature of the thread is evident but the 
parts have not separated from each other. 
Fig. 8. Pollen mother-cell of Thuja. A slightly later stage than Figs. 6, 7. The spirem has 
become quite evenly distributed throughout the cavity. Its double nature is quite evident, and in 
a few places the halves tend to separate slightly from each other. 
Fig. 9. Pinus austriaca. A complete nucleus is shown. No free ends appear, and it is certain 
that a continuous spirem exists at this time. The daughter halves of the spirem have not separated. 
Fig. 10. Same stage from Thuja. 
Fig. 11. Slightly later stage. Pinus austriaca. The spirem has contracted somewhat, becoming 
slightly thicker and more regular. It is distributed quite evenly throughout the cavity, and no signs 
are evident of a second contraction. This is the stage of the evenly distributed 1 hollow spirem ’ of 
some writers. 
Fig. 12. Pinus austriaca. Tangential view of nucleus. The spirem shows quite clearly its 
double nature. The sister halves have separated from each other at certain points. This nucleus 
represents an extreme condition that is met in only occasional cells. 
Fig. 13. A later stage from Thuja. The spirem occurs quite regularly in folds or loops. It is 
more lumpy at this time than is typical of Pinus. 
Fig. 14. Thija. The spirem has become arranged here in a very regular series of loops. Some 
of the loops are broken at the outer end. There is a dense mass at the inner ends of the loops. Such 
regular stages are not typical and are met only rarely. 
Fig. 15. Thija. The spirem has given way to a quite ragged reticulum. This stage is 
frequently met in both genera. 
Fig. 16. Thi ja. Cross-segmentation of the spirem. Some of the pieces are quite long and are 
variously oriented toward each other. 
Fig. 17. Pinus austriaca. Segments shortening and thickening not yet complete. 
Fig. 18. Same of Thuja. The nuclear membrane has disappeared, and the cytoplasm is 
becoming somewhat fibrillar. There is at this time no evidences remaining of the early longitudinal 
fission. 
Fig. 19. Same for Thuja. 
Fig. 20. Mature spindle. 
Fig. 21. Metakanesis. The members of the bivalent chromosomes are still attached at the ends 
and the longitudinal fission is not yet apparent. 
Fig. 22. Anaphase in Pinus Strobus. The retreating chromosomes are undergoing longitudinal 
fission as they pass to the poles. Straight rods, V’s, double U’s, and rods bent at the end result. 
Fig. 23. Pinus Strobus. The granddaughter segments have arrived at the poles. Some of the 
pieces are quite long drawn out. They are not closely oppressed at this time. 
Fig. 24. Daughter nuclei. The chromosomes have almost completely lost their identity. 
Fig. 25. Complete resting nucleus formed at the close of the first division. Pinus Strobus. 
Fig. 26. Spirem of the second division. The spirem is much branched and irregular. It shows 
no signs of a double nature. The nuclear membrane has already disappeared and spindle fibres have 
crowded into the cavity. 
Fig. 27. Pinus Laricio. The spirem has undergone cross-segmentation into the univalent 
chromosomes. The segments are rods either straight, hooked at the end, or bent in the middle. The 
spindle is not formed completely before cross-segmentation takes place, and the spirem does not 
undergo longitudinal fission. 
Fig. 28. Orientation of the chromosomes into the spindle plate. 
Fig. 29. The chromosomes are being brought into the plate of the spindle. 
