PLATE XIV. 
Fig. 21. 
Fig. 22. 
Fig. 23. 
Fig. 24. 
Fig. 25. 
Fig. 26. 
Fig. 27. 
Fig. 28. 
Fig. 29. 
Fig. 30. 
Fig. 31. 
Mother cell forming single pollen grain. Microspore wall 
slightly thickened; four nuclei; no dividifig walls. 
Early stage in the fusion of the degenerating nuclei. 
Later stage; degenerating nuclei crowded out toward tlio 
outer wall. 
Giant pollen grain showing two nuclei; at the left the re- 
mains of the degenerating nuclei. 
Giant microspore in which the tetrad division has not yet 
occurred. Wall thickened; nucleus in resting phase. 
Wall cleavage initiated but suppressed early. 
Cleavage suppressed at a later stage. 
A case in which cleavage is almost complete. 
Two cells resulting from cleavage. 
One member of a tetrad cut off by cleavage. 
Outline of normal pollen grain, showing relative size. 
