650 Davis.—Cytological Studies on Oenothera II. 
Fig. 24. Telophase of the heterotypic mitosis. The seven chromosomes at each pole of the 
spindle are split lengthwise. 
Fig. 25. A group of seven split chromosomes gathered at the pole of the heterotypic spindle, 
viewed from above. 
Fig. 26. A group of seven split chromosomes just before the organization of the daughter nuclei 
following the heterotypic mitosis. 
Fig. 27. An irregular distribution of chromosomes by the heterotypic mitosis. Eight chromo¬ 
somes instead of seven have been brought to the pole of the spindle ; five chromosomes (one missing) 
were found at the opposite pole. 
Figs. 28 and 29. Resting nuclei of the interkinesis between the heterotypic and homotypic 
mitoses. Seven pairs of chromosomes are present in each nucleus, mostly in the form of U s joined 
together in the bent middle region. 
Fig. 30. Nucleus of the interkinesis surrounded by a web of fibrillae preparatory to the organi¬ 
zation of the homotypic spindle. 
Figs. 31 and 32. The seven pairs of chromosomes being gathered at the equatorial plate shortly 
before the metaphase of the homotypic mitosis. 
PLATE LIII. 
Oenothera biennis. 
Figs. 33-36. Illustrating reduction phenomena in the pollen mother-cell. 
Fig- 33- Metaphase of the homotypic mitosis; seven pairs of chromosomes at the equatorial 
plate. The two spindles lie at right angles in the pollen mother-cell, so that the equatorial plate of 
one spindle is viewed from the pole. 
Fig. 34. Anaphase of the homotypic mytosis; the chromosomes of the two sets, seven in each 
group, show irregularities of form. 
Fig* 35* Telophase of the homotypic mitosis; the seven chromosomes in each nucleus still 
distinct. 
Fig. 36. Nucleus of a young pollen grain, showing the open reticulum upon which lie deeply 
staining chromatic bodies (prochromosomes?). 
Figs. 37-57. Illustrating reduction phenomena in the ovule. 
Fig. 37. Resting nucleus in megaspore mother-cell, showing large and small nucleolus, chro¬ 
matic bodies, and delicate reticulum. 
Fig. 38. Development of a much coarser reticulum from the stage shown above, chromatic 
bodies no longer distinguishable. 
Fig. 39. Nucleus filled with a dense reticulum just before the advent of synapsis. 
Fig. 40. The synaptic contraction under way. 
Fig. 41. A synaptic knot. 
Figs. 42 and 43. The thickened threads which emerge with the loosening of the synaptic knot. 
Fig. 44. Further shortening and thickening of the threads to form the spireme. 
Fig. 45. A segmented spireme. 
Figs. 46 and 47. The chromosome segments, for the most part still arranged end to end. 
Fig. 48. Chromosome segments gathered in a close group bearing a superficial resemblance to 
a synaptic knot, apparently the stage termed by some authors a ‘ second contraction ’. 
Fig. 49. Bipolar spindle, the fourteen chromosomes gathered in an irregular group. 
Figs. 50 and 51. Metaphase of the heterotypic mitosis; the chromosomes bent mostly in the form 
of thickened V’s. 
Fig. 52. Telophase of the heterotypic mitosis ; the chromosomes at the poles of the spindle are 
split lengthwise. 
Fig- 53- Resting nucleus of the interkinesis between the heterotypic and homotypic mitoses. 
Seven pairs of chromosomes are present, mostly in the form of U’s joined together in the bent middle 
region. 
Fig. 54* Prophases of the homotypic mitosis in companion cells, showing multipolar spindles 
and the seven pairs of chromosomes. 
Fig* 55. Metaphase of the homotypic mitosis. 
