Graham.— Nuclear Division of Preissia commutata . 679 
Figs. 9, 10. Later ; the spireme is of even thickness. 
Figs. 11, 12. Early prophase, showing hyaline kinoplasmic caps at elongated ends of nucleus. 
Figs. 13, 14. Segmented spireme. Nuclear membrane intact. Nucleolus shows no sign of 
vacuolization. Spindle fibres have appeared in the hyaline caps. A granule lies at the apex of the 
fibres in Fig. 13. 
Fig. 15. Segments of the spireme are shortening and thickening. 
Figs. 16, 17. Metaphase with the undivided chromosomes. 
Figs. 18, 19, 20. Early anaphase. The oval chromosomes moving towards the poles. 
Fig. 2r. Polar view of early anaphase ; at same stage as shown in Fig. 20. 
Fig. 22. Polar view at metaphase, cut slightly obliquely. Eight chromosomes are seen. 
Fig. 23. The chromosomes at the poles elongate. The first indication of a cell plate. 
Fig. 24. The chromosomes at the poles are crowded. The cell plate is more distinct. 
Figs. 25, 26. The chromosomes elongate and their identity is lost in the formation of the reticulum. 
Fig. 27. The daughter nuclei in. which there is a fine reticulum. Chromatin granules lying on 
the linin or free from it. There is a well-defined nucleolus and a definite nuclear membrane. 
PLATE LV. Sporogenesis. 
Fig. 23 was drawn using a Zeiss oil-immersion, numerical aperture 1*30, and a 6 Zeiss compen- 
sating ocular. Figs. 1, 7,^4, 15, 18, 19, and 25 were drawn using the same objective and an 8 
compensating ocular, magnification 1,430. Figs. 2, 3, 4, 5, 6, 8, 9, 10, 11, 12, 13, 16, 17,20, 21,22, 
24, and 26 were also drawn using the same objective but a 12 Zeiss compensating ocular, magnifi- 
cation 2,040. 
Fig. 1. A mature spore mother-cell. The resting spherical nucleus has a close reticulum with 
chromatin knots at its angles. Groups of plastids lie in the cytoplasm. 
Fig. 2. Enlarged nucleus. The masses of chromatin becoming more conspicuous and the 
reticulum thickening. Parts of the latter may be traced for some distance. 
Fig. 3. Leptonema spireme, some portions of which lie parallel to each other. The chromatin 
bodies larger than in stage represented in Fig. 2. 
Fig. 4. Synapsis. The chromatin bodies are of equal size and are very conspicuous in the 
synaptic knot. 
Fig. 5. Recovery from synapsis. The spireme as it emerges from synapsis is very slender. 
Fig. 6. The spireme is distributed throughout the nuclear cavity, and the chromomeres lie at 
equal distances on it. 
Fig. 7. The spireme somewhat thickened. The chromomeres present a bead-like appearance. 
Figs. 8, 9. The spireme has thickened and is contracted across a broad plane of the nuclear 
cavity. At this time it shows a split. 
Fig. 10. A segmented spireme showing the split formed at the stage represented in Figs. 8, 9. 
Fig. 11. The segments of the spireme are shortening and thickening. The split is still evident. 
The nucleolus has disappeared and the nuclear membrane is intact. 
Fig. 12. The chromosomes have become short and thick. 
Fig. 13. Metaphase showing broad, blunt spindle. 
Figs. 14, 15, 16. Anaphase. 
Fig. 1 7. Late anaphase, showing two parted chromosomes. 
Fig. 18. The chromosomes at the poles are as yet distinct. 
Fig. 19. Reconstruction of. daughter nuclei, showing a slight reticular appearance. The 
nucleolus formed and the chromatin granules present. Indication of the first wall. 
Figs. 20, 21. Daughter nuclei in prophase. Polar caps of spindle fibres very prominent. 
Figs. 22, 24, 25. Hyaline polar caps on the spore mother nucleus. 
Fig. 23. Section showing three of the spore nuclei ; the fourth nucleus and the first wall laid 
down is in another section. 
Fig. 26. Coarse strands of cytoplasm extend from groups of plastids across the hyaline cap to 
the nuclear membrane. 
3 A % 
