Gates.—Pollen Formatio 7 i in Oenothera gigas. 939 
Fig. 34. Homotypic metaphase. In this anther all the mother-cells had proliferated cell-walls 
and very broad spindles. The chromosomes are all clearly bipartite, x 2,100. 
Fig. 35. Another homotypic metaphase, showing narrow spindles and smooth mother-cell wall, 
x 2100. 
Fig. 36. Homotypic metaphase, in which only two chromosomes, one on each spindle, show 
their bivalent character. Thirteen chromosomes visible in left-hand spindle, and a nucleolus 
persists in the cytoplasm, x 2,100. 
Fig. 40. Homotypic spindle in late anaphase. Spindle cut, but 12 + 13 chromosomes present, 
x 2,100. 
Fig. 41. Section of another homotypic spindle in anaphase, in which nearly all the chromosomes 
show a clear median constriction. There are also several rods and one V. x 2,100. 
Fig. 42. Homotypic telophase, showing many of the daughter chromosomes transversely con¬ 
stricted. x 2,100. 
Figs. 43 and 44. Somewhat later homotypic telophase nuclei, showing the bivalent appearance 
of many of the chromosomes. x 2,850. 
Fig. 45. Later homotypic telophase, in which the nucleus has grown larger, a nucleolus has 
appeared, and the chromosomes have begun to lose their compact structure, x 2,850. 
PLATE LXIX. 
Fig. 37. Early homotypic anaphase. Spindles very narrow. Several of the daughter chromo¬ 
somes show a median constriction, x 2,100. 
Fig. 38. Homotypic mitosis. Spindles broad and cell-wall proliferated. The spindle on the 
left shows several of the chromosomes whose halves have not yet separated. The spindle on the 
right is an early anaphase, showing in oblique view one of the groups of fourteen daughter chromo¬ 
somes. x 2,100. 
Fig. 39. Later homotypic anaphase, slightly oblique cut, showing 14 + 12 chromosomes on the 
spindle. Chromosomes partly looped and partly rod-shaped or nearly globular. Cell-wall pro¬ 
liferated. x 2,100. 
Fig. 46. Late homotypic telophase. The chromosomes are elongating and ‘stringing out’ to 
pass into the resting condition. Cell-plates not yet formed. Cell-wall proliferated, x 2,100. 
Figs. 47 and 48. Tetrads of young pollen cells within the mother cell-wall, x 525. 
Fig. 49. Young pollen grains of 0 . gigas with four interstitial bodies, x 1,275. 
Fig. 50. Similar grain, with five interstitial bodies symmetrically placed, x 1,275. 
Figs. 51 and 52. Typical four-lobed pollen grains of 0 . gigas. Nucleus amoeboid in appear¬ 
ance, cytoplasm in strands. x 1,275. 
Figs. 53 and 54. Five-lobed and seven-lobed grains, with the extra lobes asymmetrically placed, 
x 1,275. 
Fig. 55. Longitudinal section, showing a row of pollen mother-cells in interkinesis, and the 
surrounding binucleate tapetal cells. The mother-cell walls have remained in direct contact with 
the tapetal cells, x 600. 
Fig. 56. A row of mother-cells still in contact with each other, and polygonal, although under¬ 
going the reduction divisions. In the two middle mother-cells a cleavage of the cytoplasm follows 
the heterotypic mitosis, x 900. 
Figs. 57 and 58. Each figure shows two mother-cells in interkinesis. In two of the cells 
a cleavage of the cytoplasm has appeared between the daughter nuclei, and in one a small extra 
nucleus appears in the cytoplasm, x 1,125. 
Figs. 59-61. Homotypic prophase nuclei before the disappearance of the nuclear membrane. 
Most of the chromosomes are clearly in pairs, and they vary greatly in size owing to differences in 
their compactness, x 2,550. 
Fig. 72. Early homotypic telophase group of chromosomes, x 2,850. 
Fig. 73. A later stage of the homotypic telophase, after the formation of the nuclear membrane. 
Fourteen chromosomes, x 2,850. 
Fig. 74. Slightly later stage, nucleus uncut, showing fourteen chromosomes and a nucleolus, 
x 2,850. 
Fig. 75- Same as Fig. 73. Showing fifteen chromosomes and a nucleolus. In Figs. 72-75 
the chromosomes show no sign of a median constriction as in normal development, x 2,850. 
