ti2 CANNON: STUDIES IN PLANT HyBripDs 
The first maturation division in the normal cells is heterotypic, 
the second homotypic; and also amitosis occurs. | Many addi- 
tional abnormalities in the nuclei were observed ; such nuclei, how- 
ever, do not undergo division, but degenerate in the archesporial 
cell or some later stage, in every case before the first division. 
Among such irregularities a few mother-cell nuclei were observed 
with two spindles and the somatic number of chromosomes. 
COLUMBIA UNIVERSITY, 1902. 
Explanation of Plates 
PLATE 7 
Fic. 1. Microspore mother-cell. 
Fic, 2. Same. 
Fic. 3. Split spireme in prophase of first division. 
Fic. 4. a, 6, c, d, e; typical chromatin loops from the prophases of the first 
division, showing the double splitting. 
Fic. 5. Same at a later stage. 
Fic. 6, Condensation of rings into chromosomes preparatory for the first divi- 
sion ; breaking down of the nuclear wall. 
Fic. 7. Same, later stage. 
Fic, 8. A multipolar spindle which is becoming a ees one. 
Fic. 9. Metaphase of the first division. 
Fic. 10. Anaphase of the same division, somewhat to one side of the median 
line ; in the section next to this one the poles of the spindle were observed to extend 
quite to the periphery of the cell. 
Prate 8 
Fic. 11. Chromosomes in the metaphase of the first division. 
Fic, 12, a. Resting daughter-nucleus. 4. Sketch of same nucleus, from the next 
section, showing its relation to the spindle, and that of the latter to the periphery of 
the cell. 
Fic. 13. Daughter-nuclei; the reticular character of the cytoplasm not well 
shown; the presence of inter-nuclear fibrillae, the remains of the continuous fibers, is 
indicated. 
Fic, 14. Early anaphase of second division; the more heavily shaded portion 
of the cytoplasm indicates the position of the perinuclear zone; the fibrillar layer in 
the cytoplasm is shown. 
Fic, 15. Metaphase of the second division. 
Fics. 16-19 are of abnormal (amitotic) nuclear division of spore mother-cells. 
Fic. 16. Daughter-nuclei. 
Fic. 17. Nuclei of different sizes. 
Fic, 18, 2 and 4. Tetrads with smaller nuclei scattered in the cytoplasm. 
Fic, 19, 2 and 6. Equal and unequal direct division of the nucleus of the mother- 
cell. 
Norte. — The primitive character of the cytoplasm is shown in Figs. 16, 17, 184 
and 184, 
