570 Davis. — Cytological Studies on Oenothera . /. 
Fig. 6. Metaphase of mitosis in archesporial cell viewed from the pole of the spindle, fourteen 
chromosomes. 
Fig. 7. Anaphase of mitosis in archesporial cell, showing V-shaped chromosomes. 
Fig. 8. Pollen mother-cells after the final mitosis in the archesporium, nuclei with chromatic 
bodies and large nucleoli. 
Fig. 9. Nucleus before synapsis, chromatic bodies connected by a delicate reticulum. 
Fig. 10. Later stage, the reticulum more prominent in preparation for synapsis. 
Fig. 11. Nucleus just before the beginning of synapsis, a close reticulum present. 
Fig. 12. Early stage of synapsis, system of threads developing from the reticulum shown in 
Fig. 11. 
Fig. 13. Synaptic contraction well under way. Most of the threads are in closely twisted coils 
near the large nucleolus, certain very delicate threads lie close to the nuclear membrane. 
Fig. 14. Synapsis, the loops extending from the synaptic knot consist of rows of granules 
(chromomeres ?). 
Fig. 15. Synapsis, coiled and looped threads around the large nucleolus, very delicate threads 
close to the nuclear membrane. 
Figs. 16-18. Synapsis, the threads thickening. 
Fig. 19. Synaptic contraction almost complete, showing the dense knot, the loops extending 
into the nuclear cavity, and some delicate threads lying close to the nuclear membrane. 
Fig. 20. Synaptic contraction probably complete, thickened loops extending from the 
synaptic knot. 
Figs. 21 and 22. Complete synaptic contraction of the dense type, the loops represented by 
protrusions from the synaptic knot. 
Fig. 23. Contracted synaptic mass ready to loosen up, the loops and prominent protrusions 
probably now organized into ring-shaped bivalent chromosomes. 
Fig. 24. A stage in the loosening of the synaptic knot. The loop-like structures are chromatic 
' rings. 
Figs. 25 and 26. The ring-shaped chromosomes shortly after their emergence from the synaptic 
knot. The rings are large at this stage. 
Fig. 27. Approaching the phase of diakinesis. Most of the rings are still clustered around the 
large nucleolus. 
Fig. 28. Diakinesis, the rings now much more condensed than when first organized (Figs. 24-26). 
Fig. 29. A group of rings, certain of which are linked together — a stage in the emergence 
of the rings from the synaptic knot similar to Figs. 24-26. 
Fig. 30. A group of linked rings. 
Fig. 31. Early prophase of the heterotypic spindle, large nucleolus still present. The nuclear 
membrane has disappeared, chromatic rings distributed in the nuclear cavity, which is surrounded 
by a web of fibrillae. 
Fig. 32. Multipolar spindle, chromatic rings gathered in the centre of the nuclear cavity. 
Fig- 33- Certain chromatic rings show clearly their bivalent nature, being composed of two 
thickened semicircular halves. 
Fig. 34. The seven bivalent ring-shaped chromosomes gathering at the equatorial plate. 
Fig. 35. Some of the chromosome rings densely clustered it the equatorial plate as if they 
might be linked together. 
Fig. 36. Pollen mother-cell in prophase of the heterotypic mitosis, showing the relation of the 
multipolar spindle to the surrounding alveolar cytoplasm. Sevenbivalent chromosomes are gathered 
in the centre of the spindle. 
PLATE XLII. 
Oenothera grandijlora. 
Fig. 37. Pollen mother-cell at metaphase of the heterotypic mitosis, the two sets of sporophytic 
chromosomes still united in pairs forming rings. The similarity of the chromosomes in form and 
size is clearly shown. 
Fig. 38. Another metaphase illustrating the fact that certain rings may lag behind the others in 
completing the separation of their halves (sporophytic chromosorms). 
Fig. 39. Early anaphase of the heterotypic mitosis, showing the V-shaped sporophytic 
chromosomes, all of similar form and size. 
