Chromosomes in Pollen Mother-cells. 
34 7 
Lilium Mart agon. 
Fig. 15. Nucleus of a young pollen mother-cell at the close of the last sporogenous division. 
The chromatin lumps composed of smaller but distinct granules show a tendency to be grouped 
about the several nucleoli, from which thicker and thinner strands of linin tend to radiate. 
Fig. 16. A later stage in presynaptic growth. The chromatin has increased in quantity, and 
the nucleus has become greatly enlarged. 
Fig. 17. Similar to the preceding ; chromatin uniformly distributed in lumps or masses. 
Fig. 18. A similar stage. The nucleus became differentiated in such a way as to show both the 
chromatin and the linin of the lumps. 
Fig. 19. Beginning of synapsis. Here the chromatin, in the form of finely divided granules of 
rather uniform size, is arranged in a spirem-like net, which seems to show some orientation with 
reference to one of the flattened nucleoli. The nucleolus or nucleoli in such nuclei are flattened 
against the nuclear membrane (the sickle stage of older literature). 
Fig. 20. A similar condition of the chromatin, showing a further step in the contraction. 
Fig. 21. Complete synapsis of such nuclei. 
Fig. 22. Nucleus undergoing synapsis in which the chromatin remained in the larger lumps. 
Fig. 23. Complete synapsis of this condition. 
Fig. 24. The synaptic mass loosening up. The double row of chromomeres show that the 
thread is longitudinally split or undergoing this process. 
Fig. 25. The hollow spirem just after synapsis, showing longitudinal fission. All chromomeres 
do not seem to be paired. Free ends are due to cutting. 
Fig. 25 a. A portion of the thread more enlarged. 
Lilium candidum. 
Fig. 26. Similar, or a little later than Fig. 25. The thread stained more uniformly, and the 
chromomeres are not readily seen. This figure includes more of the nucleus than Fig. 25. 
Fig. 27. Hollow spirem in which the rearrangement into loops and the central entanglement 
have begun. At this stage the longitudinal halves of the spirem tend to divaricate for longer or 
shorter distances. This is not true in all nuclei. 
Fig. 28. A later stage. The spirem is still quite slender, having shortened and thickened only 
a very little. The formation of the loops is evident, and the central entanglement about the 
nucleolus is more pronounced. 
Figs. 29, 30, 31. Later stages. The parallel sides of loops have come closer together. The 
longitudinal halves of the thread that may have divaricated in an earlier stage have come together 
again, so that traces of this fission are becoming more difficult to observe. Cross segmentation now 
takes place. In Fig. 30 this may be complete ; in Figs. 29 and 31 the central entanglement is too com- 
plicated to admit of a clear view. At this stage the spirem is usually as entangled as Fig. 29 and 
even more so. From the stage of Fig. 30, i.e. after cross segmentation, the greatest shortening and 
thickening of the chromatin takes place. 
Fig. 32. The bivalent chromosomes are beginning to separate and to distribute themselves 
within the nucleus. 
Fig- 33- Chromosomes distributed. The formation of the spindle begins at this stage. The 
loop-like character of the majority of the chromosomes is still seen. In this and earlier stages 
delicate linin threads extend out from the chromosomes that connect them with each other and with 
the nuclear membrane. 
Tradescantia virginica. 
Fig. 34- Presynaptic stage ; chromatin in larger or smaller groups or lumps. 
Fig. 35. The loosening up of the synaptic mass. The loosening spirem presents a rather 
regular arrangement, the so-called * bouquet’ stage. The longitudinal fission is seen in places. 
Figs. 36 and 37. The second contraction figure. Cross segmentation almost complete in 37. 
All traces of the longitudinal splitting have disappeared from sight. 
Figs. 38, 39. The chromosomes distributed in nucleus prior to formation of spindle. The 
segments or univalent chromosomes are frequently attached end-to-end, forming a zig-zag row of 
sausage-like pieces. 
Fig. 40. A stage in the formation of multipolar spindle. The chromosomes are crowded 
together somewhat, a usual phenomenon at this stage. Some still show the end-to-end attachment. 
This persists in some cases even to the metakinesis (see author’s figures, ’03). 
