Beer. — Studies in Spore Development. III. 
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EXPLANATION OF PLATES LI-LIII. 
Illustrating Mr. Beer’s paper on Spore Development in Equisetum. 
All the figures were drawn with the aid of a camera lucida. Zeiss’s apochromatic objective 
2 mm. (apert. 1*40) and compensating ocular 18 were used for making the drawings. The magnifi- 
cation in all cases is about 2,700 diameters. 
PLATE LI. 
Fig. 1. Archesporial cell with ‘ resting ’ nucleus. 
Fig. 2. Archesporial cell ; prophase of division. 
Figs. 3, 4. Archesporial cells ; later stages of prophase of premeiotic division. 
Fig. 5. Spireme of premiotic division. 
Fig. 6. Metaphase showing the longitudinal division of the chromosomes. 
Fig. 7. Metaphase showing the separation of the longitudinal halves of the chromosomes. 
Fig. 8. Anaphase of premeiotic division. 
Fig. 9. Daughter chromosomes massed at the two poles ot the spindle. 
Figs. 10, 11. Telophase of premeiotic division. 
Fig. 12. Commencement of prophase of first meiotic division. Open reticulum. 
Fig. 13. Beginning of synapsis. 
Fig. 14. Nucleus shortly before synapsis, showing fusion of nucleoli. 
Fig. 15. Synapsis. 
PLATE LII. 
Fig. 16. Nucleoli from ‘resting’ nuclei of archesporial cells. 
Fig. 17, a, b, c. Spireme emerging from synapsis. The longitudinal split in the spireme is 
shown. 
Figs. 18, 19. Spireme. 
Fig. 20. Spireme segments with longitudinal division. 
Figs. 2i, 22. Second contraction. 
Figs. 23, 24. Stages in the development of the heterotype chromosomes. 
Fig. 25. Heterotype chromosomes in diakinesis. 
Fig. 26, a-h. Various forms of heterotype chromosomes. 
Fig. 27. Fusion of nucleoli previous to synapsis. 
Fig. 28. Multipolar polyarch spindle of first meiotic division. 
Fig. 29. Multipolar diarch spindle developed from the multipolar polyarch structure. 
Fig. 30. Chromosomes arranged on the spindle during the metaphase of first meiotic division. 
PLATE LIII. 
Fig. 31. Fully developed bipolar spindle. 
Fig. 32. Anaphase of first meiotic division. 
Fig. 33. Conclusion of anaphase. 
Figs. 34, 35. Telophase of first meiotic division. 
Fig. 36. Details of chromosomes during telophase, showing vacuolation and branching of their 
substance. 
Fig. 37. Nucleus during interkinesis. 
Figs. 38, 39. Prophase of second meiotic division. 
Figs. 40, 41. Two modes of development of spindle during second meiotic division. 
Fig. 42. Prophase of second meiotic division, showing chromosomes longitudinally divided. 
Fig. 43. Metaphase of second meiotic division. 
Fig. 44. Anaphase of second meiotic division. 
Figs. 45, 46. Telophase of second meiotic division. 
Fig. 47 * Spore of Equisetum at early stages of its development. 
