434 MINNESOTA BOTANICAL STUDIES 



EXPLANATION OF PLATES 

 PLATE XLIII 



Figures 1-9. Stages in reduction division of pollen mother cell. X 700. 

 L Before synapsis. 



2. Synapsis. 



3. Late prophase, after synapsis. 



4. Homotypic prophase and half of heterotypic diaster. 



5. Two homotypic metaphases, each showing six chromosomes. 

 6-8. Homotypic metaphase with six chromosomes. 



9. Homotypic anaphase. 



10. End view of one-nucleate pollen grain. X 700. 



11. Side view of two-nucleate pollen grain. X 300. 



12. Pollen grain and part of pollen tube on stigma sixteen hours after 



opening of flower. X 300. 



13. Cross-section of young ovar}-. X 28. 



14. Ovule (a of fig. 13) with archesporial cell in detail. X 700. 



15. Tip of ovule with tapetal cell and megaspore mother-cell in detail. 



X 700. 



16. Tip of ovule with megaspore mother-cell in detail. X 700. 



17. Tip of ovule with metaphase of heterotypic division of megaspore 



mother-cell. X 300. 



18. Chromosomes (in outline) and spindle fibers of preceding. X 1225. 



19. Cross-section of loculus : a. ovule containing four megaspores. X 12. 



PLATE XLIV 



20. Ovule a of preceding. X 300. 



21. Four megaspores and a nucellar cell of preceding in detail. X 700. 



22. Megaspores in detail, during breaking down of some. X 700. 



23. Part of nucellus with functional megaspore in detail, remnants of 



three others, and tapetal cells beginning to break down. X 700. 



24. Ovule containing the preceding. X 12. 



25. Part of nucellus of preceding. X 300. 



26. Part of nucellus after first division of functional megaspore. X 300. 



27. Part of nucellus with tapetal layer disintegrated. X 300. 



28. Aletaphase in polar view in nucellar cell of preceding; twelve chro- 



mosomes in outline. X 1225. 

 ^■9. Embryo sac with eight nuclei. X 300. 



PLATE XLV 



30. Embryo sac during fusion of polar nuclei near chalazal end. X 300. 



31. Ovule containing preceding: a, layer probably containing substances 



which direct growth of pollen tube. X 12. 



