140 Arlow Burdette Stout, The individuality of the chromosomes, etc. 



Fig. 22. Synapsis. 



Fig. 23. Pachyneme stage of post-synapsis. 



Fig. 24. Diakinesis. Chromosomes in pairs at the periphery. Spirem some- 

 what in evidence. 



Fig. 25. Stage following diakinesis. Bivalent spirem drawing in from the peri- 

 phery. Lower part of the nucleus in cell a not shown. 



Fig. 26. A stage somewhat later than the one shown in fig. 25. Spirem is more 

 toward the center of the nucleus. The bivalent chromosomes appear more compact. 



Fig. 27. Polar view of the equatorial plate of the heterotypic division: 37 pairs 

 of chromosomes in view; most of them in profile. The serial arrangement can be traced 

 for some distance. 



Fig. 28. Lateral view of the equatorial plate of the heterotypic division just 

 previous to the separation of the paired chromosomes. 



Fig. 29. Telophase of the heterotypic division. 



Fig. 30. Homoeotypic divisions ; both polar and lateral views shown. 



Fig. 31. Cell showing the four microspore nuclei. Only the large central one 

 will develop; the three at the apex will eventually disintegrate. All show the chro- 

 mosomes. 



Fig. 32. Stage showing the elongated generative cell. The vegetative nucleus 

 lies at a lower level and is only shown in part. 



Fig. 33. Median section through a pollen grain showing vegetative nucleus, 

 generative cell which is now rounded, and two of the cells at the apex. Chromosomes 

 are present in all the nuclei and the serial arrangement is in evidence. 



Fig. 34. Portion of a pollen grain showing generative cell in prophase. The 

 spirem consists of individual chromosomes. 



Fig. 35. Showing telophase in the division of the generative cell. At the apex 

 of the grain is shown a portion of the plate formed by the disintegrating nuclei. 



Fig. 36. Portion of a mature pollen grain showing nucleus of the vegetative cell 

 and the two germ cells. The chromosomes are visible in all three nuclei. 



