NUCLEAR OSMOSIS AS A FACTOR IN MITOSIS. 161 
Yucca. 
Kig. 26. A median section of a microspore mother-cell, showing the nuclear vacuole at its maximum size. 
Fig. 27. The same, showing a considerable reduction in the volume of the nuclear vacuole and an 
indication of radiating kinoplasmic threads in the surrounding cytoplasm. 
Fig. 28. The same at a slightly later stage, with the kinoplasmic threads much more sharply defined. 
The nuclear vacuole is considerably less than a fourth of its original volume, and the nuclear wall is still 
intact. 
Fig. 29. Another example of the same condition, but slightly older. 
Fig. 30. The nuclear membrane still intact, and the kinoplasmic threads appear in groups or sheaves. 
Fig. 31. The chromosomes are crowded together by the enclosing of the nuclear membrane about them. 
An irregular multipolar condition has been reached. 
Fig, 32. The nuclear membrane has completely enveloped each chromosome, so that each of these bodies 
is now provided with a system of kinoplasmic threads. 
Fig. 33. The mature spindle with the chromosomes at the equator. 
HEDERA. 
Fig. 34. A median section of a microspore mother-cell showing the nuclear vacuole at its maximum'size. 
Fig. 35. The same, showing a considerable decrease in the volume of the nuclear vacuole and the 
appearance of an incomplete zone of kinoplasm. 
Fig. 36. The same, showing the kiuoplasmic threads radiating from the nuclear membrane and much 
more sharply defined. There is a still further decrease in the nuclear vacuole, and the nuclear membrane 
is intact. 
Fig. 37. A distinct but irregular multipolar condition. The karyolymph in the nuclear vacuole has 
almost completely diffused, and the chromosomes are consequently crowded together by the receding nuclear 
membrane. 
Fig. 38. Each chromosome has become enveloped by the nuclear membrane and consequently furnished 
with a system of kinoplasmic fibrils. 
Fig. 39. The mature spindle with the chromosomes at the equator. 
ALLIUM. 
Fig. 40. A median section of a vegetative cell in the root tip. The nucleus is quite large and prepared 
for mitosis. The chromosomes are almost organised. 
Fig. 41. A slightly later stage of the same. The kinoplasm appears in the section as narrow crescents 
of threads which appear at opposite sides of the nucleus. There has been a slight decrease in the size of 
the nucleus, 
Fig, 42. A further decrease in the volume of the nucleus, and a corresponding increase in the 
differentiation of the kinoplasm. 
Fig. 43. The same a little later, showing the polar caps. 
Fig. 44. Another section of the same. 
Fig. 45. The polar caps completely organised, with a very obvious diminution in the volume of the 
nuclear vacuole. The nuclear membrane is still intact. 
Fig. 46. The nuclear membrane has closed in about each chromosome. 
Fig. 47. Showing the connection of the kinoplasmic fibrils to the membrane enveloping each chromosome. 
Fig. 48. The mature spindle with the chromosomes at the equator. 
Fig. 49. The daughter chromosomes have moved to the poles of the spindle. Numerous threads of 
kinoplasm stretch between the chromosomes at opposite ends of the spindle. 
Fig. 50. The grouping together of the daughter chromosomes at the poles. 
Fig. 51. The same a little later. 
Fig. 52. The vacuolisation of the daughter chromosomes, accompanied by a relaxation of the tension in 
the cell. This relaxation is expressed in the loose curvature of the kinoplasmic threads, 
Fig. 53. The daughter nuclei fully developed. The development of the large nuclear vacuoles has 
relaxed the tension in the cytoplasm completely, and all kinoplasmic threads have vanished. 
TRANS. ROY. SOC. EDIN., VOL. XLVIII. PART I. (NO. 7). 25 
