PLATE C 



I. — Late anaphase of the heterotypic division. The cytoplasm is rounding up 

 from the mother cell wall and is partially surroimded by a thick gelatin-like sheath. 

 X 2,000. 



2. — Chromosomes on the equatorial plate of the homeotypic division. 



3. — A portion of an anther in the tetrad stage, showing the microspores embedded 

 in the gelatin-like sheath. The original mother cell walls are still present. 



4. — A tetrad at the same stage as those shown in figure 3. The mother cell wall 

 is not shown. X 2,000. 



5. — A microspore shortly after liberation from the tetrad. X 2,000. 



6. — A liberated microspore in which growth has commenced. X 2,000. 



7. — A later stage than figure 6, showing the slight thickening of the wall and 

 the irregularities due to growth of the wall. X 2,00c. 



8. — Microspore growth completed previous to division of the microspore nucleus. 

 X 2,000. 



9. — A section through a microspore nucleus in prophase showing the continuous 

 univalent spireme. X 3,280. 



. 10. — Another section of the same nucleus, showing the first stages of the disappear- 

 ance of the nucleolus. The nucleolar strands are attached to the spireme. X 3,280. 



II. — Metaphase of the division of the microspore nucleus. A spindle in this posi- 

 tion results in the nuclear arrangement shown in figure 15. The thickened extine is 

 shown. X 2,000. 



12. — F. virginiana. Anaphase in the division of the microspore nucleus. The 

 spindle lying parallel to the wall results in the nuclear arrangement shown in figiu-e 14. 

 X 2,000. 



13. — Telophase of the division of the microspore nucleus. The wall which eventu- 

 ally surrounds the generative nucleus is not always apparent at this time. 



14. — A later stage than figure 13 in which the generative cell has been definitely 

 cut off. X 2,000. 



15. — A yotmg pollen grain shortly after division, showing an increase in cytoplasm 

 content. The thickened extine is shown. X 2,000. 



16. — End view of a pollen grain showing the pattern of the laminate layers shown 

 in figure 15 and Plate D, figures i, 6, and 15. The arrows mark the ends of the three 

 sutures which bear the germ pores. 



