973 
Oenothera Lamarckiana and 0 . gigas. 
Fig. 29. A group of seven chromosomes, still undivided, at the pole of a heterotypic spindle. 
Fig. 30. An exceptional case in which eight split chromosomes, instead of the normal number 
seven, are clearly present at the pole of a heterotypic spindle. 
Fig. 31. Early telophase of the heterotypic mitosis showing the seven split chromosomes ; 
nucleoli have not yet appeared. 
PLATE LXXII. 
Figs. 32-45, Oenothera Lamarckiana . 
Fig. 32. Pollen mother-cell following the heterotypic mitosis. 
Fig. 33. Resting nucleus of the interkinesis between the heterotypic and homotypic mitoses. 
The seven pairs of chromosomes are shown, mostly in the form of U’s joined in the bent middle 
region. 
Figs. 34 and 35. Multipolar spindles in the prophases of the homotypic mitosis. The seven 
pairs of chromosomes now appear in a much more condensed form than during the interkinesis. 
Fig. 36. Metaphase of the homotypic mitosis; seven pairs of chromosomes at the equatorial plate. 
Fig. 37. Early anaphase of the homotypic mitosis; the chromosomes in two sets, seven in 
each group. 
Figs. 38 and 39. Late anaphase and early telophase of the homotypic mitosis. The seven 
chromosomes at each pole exhibit irregularities of form. 
Fig. 40. Pollen mother-cell in telophase of the homotypic mitosis; the seven chromosomes 
distinct in each nucleus. 
Figs. 41 and 42. Telophases of the homotypic mitosis. The chromosomes are elongating and 
becoming irregular in form preparatory to the development of the chromatic network. 
Fig. 43. Nucleus of a young pollen-grain, showing the open reticulum with certain deeply 
staining regions that probably represent chromosome centres or prochromosomes. 
Fig. 44. Pollen mother-cell in which there was an irregular distribution of the chromosomes 
during the homotypic mitoses, resulting in the formation of two small extra nuclei each containing 
three chromosomes. 
Fig* 45* Young pollen-grain with a small extra nucleus, the result of an irregularity in the 
homotypic mitosis similar to the sort illustrated in Fig. 44. 
Figs. 46-63, Oenothera gigas. 
Fig. 46. Telophase following a mitosis in an archesporial cell; chromosomes still evident. 
Compare with Fig. 1. 
Figs. 47 and 48. Resting nuclei in pollen mother-cells, showing large nucleoli, chromatic 
bodies, and delicate reticula. 
Figs. 49 and 50. Nuclei filled with dense reticula, chromatic bodies no longer distinguishable. 
Fig. 51. Nucleus shortly before the advent of synapsis. Compare with Fig. 4. 
Fig. 52. The synaptic contraction well under way, the threads and meshes of the reticulum 
becoming drawn into a close mass. 
Figs. 53 and 54. Closely contracted synaptic knots. Compare with Figs. 8 and 9. 
Fig. 55. The thickened threads which emerge with the loosening of the synaptic knot. Com¬ 
pare with Figs. 10 and n. 
Fig. 56. Further shortening and thickening of the threads to form the spireme. Compare with 
Fig. 12. 
Fig. 57. A spireme just previous to the process of segmentation. 
Fig. 58. Spireme with constrictions which show that the process of segmentation has begun. 
Compare with Fig. 14. 
Fig. 59. A segmented spireme ; the chromosome segments for the most part clearly arranged end 
to end in the form of a chain. 
Figs. 60-62. Examples of the ‘ second contraction’. Segmentation has just begun in the 
spireme of Fig. 60. Compare with Figs. 18-20. 
Fig. 63. Another form of the ‘ second contraction ’; the spireme segments are more loosely 
associated. Compare with Fig. 21. 
3 s 
