TETRAD-DIVISION 



49 



Pollen-mother-cells of a Lily in course of division, somewhat diagrammatic, i. 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, n. 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.) 



