TETRAD-DIVISION 
49 
Pollen-mother-cells of a Lily in course of division, somewhat diagrammatic. 1. Mother- 
cell with resting nucleus. 2. The segregation of the chromosomes. 3. Synapsis. 
4. Double threads already beginning to coalesce. 5. The spirem derived from the 
coalescent double-thread, apparently a single thread. 6. Subsequent separation of 
the threads. 7. The spirem transversely segmented, double chromosomes. 8. Diakinesis. 
9. Initiation of multi-polar spindle. 10. Spindle of the mother-nucleus, the nuclear plate 
composed of double-chromosomes. 11. Reduction-division, the separating chromosomes 
showing a partial separation of their longitudinal halves. 12. Formation of daughter- 
nuclei. 13. The longitudinal halves of the chromosomes (daughter-chromosomes) are 
disposed in the nuclear spindles connected in pairs. 14. Daughter-nuclear-spindles. 
15. Separation of the daughter chromosomes, 16. Formation of the nuclei of the second 
generation. X about 800. (After Strasburger.) 
