198 Darling: Sex in dioecious plants 



8. A later stage showing two bodies appearing at a time. 



9- The thread well iortned, the last bodies becoming free from the nucleolus. 



10. The thread is formed; a chromosome which stains very lightly appears com- 

 ing from the nucleolus. 



11. The thread begins to knot up toward one side of nucleus. 



12. The contraction phase with the thread in a knot at one side of nucleus, asso* 

 ciated with the nucleolus. The chromosome upon the nucleolus takes the chromatin 



stain more deeply. 



13. The thread unfolding; the chromosome on the nucleolus shows its bivalent 

 character. The cytoplasm begins to pull away from the cell wall, 



14. A little later stage, in which a chromatin body is coming from the nucleolus 

 like those in 3 ; this is not a very common phenomenon. 



15. The threads begin to become parallel and a thickening appears preparatory to 

 the formation of the first chromosome from the thread. 



Plate 13 



m 



16-19, Successive stages of formation of the eight chromosomes from the thread. 

 The chromosome remains attached to the nucleolus but still shows its bivalent character. 



20. The eight chromosomes from the thread are well formed. One chromosome 

 nearly freed from the nucleolus, three others appearing in succession. 



21. One chromosome entirely freed from the nucleolus, a second merely attached 

 by a thread, a third and fourth just appearing. 



22. Three chromosomes freed from the nucleolus, the other two apparent at oppo- 

 site ends of the nucleolus. Cytoplasm well drawn away from the cell wall. 



23. Polar view of the thirteen chromosomes in metaphase, showing some difference 

 n size of the chromosomes. 



24. a and 3. Polar views of a single nucleus in anaphase, in which each chromo- 

 some has split and each half is moving toward opposite poles. 



25. Early stage of reconstruction of the daughter nuclei, showing the one large 

 chromatin mass in each, together with several smaller ones which vary in size and stain- 

 ing capacity. The smaller masses seem to pour their chromatin into large ones. 

 Remains of nucleolus may be seen in cytoplasm. 



26. A later stage of reconstruction showing nearly all of the chromatin lodged in 

 one large mass in one cell and in one large and one small in the other. 



Plate 14 



27. An uncommon stage, in which there are two chromatin bodies in each daughter 

 nucleus. In one nucleus they appear to be of more equal size than in the other ; the 

 large mass in one appears somewhat irregular due to the fusion of the smaller masses. 



28. A very common stage, in which one nucleus has the one chromatin body, the 

 other the large and small one. 



29. All of the chromatin has fused into one large mass in each nucleus. The 

 small non-staining bodies appear around the wall of the nucleus. 



30. Early stages preparatory to the second division. The bivalent chromosomes 

 just appearing on the nucleolus, 



31. Later stage showing in one of the nuclei the secondary chromatin mass giving 

 up its chromatin in small spherical bodies to form the other chromosomes. 



32. A stage just previous to the breaking down of the nuclear wall ; the bivalent 

 chromosomes clearly visible, coming from the nucleolus. 



