iQif>l NOTHNAGEL— REDUCTION DIVISIONS 



475 



Fig. 5. — Typical resting nucleus of the pollen mother cell; chromatin 

 aggregations comparatively large, and the connecting strands very fine. 



FlGS. 0, 7. -Somewhat later stages in which the anastomoses are dis- 

 appearing, connecting strands between the parallel sides becoming very fine 

 in structure, and the sides of the ladder growing more uniform. 



FlG. 8.— Late resting stage; the connecting strands disappearing, leaving 

 two parallel daughter spircms. 



Fig. 9 — Early synapsis; the two parallel daughter spirems approaching 

 each other and at places approximating. 



Fig. 10.— A later stage; the double nature still plainly discernible in many 

 places. 



Fig. 11.— Complete synapsis, showing the coiled spirem in which approxi- 

 mation has been completed. 



Fig. 12. — Same as above, but magnification not so great. 



Fig. 13. — Coming out of synapsis. 



Fig. 14.— Late coming out of synapsis, the double row of granules still 

 visible, these being the remains of the larger chromatin aggregations as seen 

 on the ladder-like structures. 



Fig. 15.— Spirem; traces of the granules of early prophase showing. 



Fig. 16.— Hollow spirem; granules evident and occasionally a split where 

 approximation was not complete. 



PLATE XXIX 



Fig. 17. — Beginning of second contraction; the spirem very heavy. 



Fig. 18. — Second contraction consisting of radiating loops. 



Fig. 19.— Segmentation beginning at the outer bend of the loop; a and 

 a' formerly being continuous, likewise b and b' ; although at this time a and b 

 are twisting about each other to form the bivalent. 



Fig. 20.— Further contraction of the chromatin mass in which the free 

 ends of the bivalents are radiating out from the mass. 



Fig. 21. — Loosening up of the bivalents. 



Fig. 21.V and .v.— Showing the gradual thickening of the bivalents. 



Fig. 22. — Eight bivalents evenly scattered within the nuclear cavity in 

 which some are seen to be open at both ends, others closed at one end, while 

 still another, lying under the others, is seen to be stretched out instead of 

 twisted. 



Fig. 23.— Beginning of the liber formation outside the nuclear membrane 

 which accompanies the third contraction; also the disappearance of the 

 nuclear membrane. 



Fig. 24. — A slightly later stage; nuclear membrane apparently gone on 

 one side of the nucleus. 



Fig. 25. — Later; the fibers in contact with part of the chromosomes; 

 nuclear membrane entirely disappeared; the multipolar complex begun. 



Fig. 26. — A later stage. 



