482 Woolery.—Microspore Mother-cells of Smilacina racemosa . 
Fig. 15. Segmentation into bivalent chromosomes has just taken place. Some bivalents are 
formed by approximation of limbs of loops and some by the approximation of the separate chromo¬ 
somes. 
Fig. 16. Second contraction stage. Longitudinal splits of the thread are appearing. Looping 
and twisting of threads is taking place. 
Fig. 17. Bivalent chromosomes in various shapes and forms. (Cf. photograph of model on 
p. 8.) 
Fig. 18. Segmented stage. The bivalent chromosomes are of different sizes. One chromosome 
of each of three bivalents is drawn out as if by some tension. 
Fig. 19. Bivalent chromosomes, one with two loops but with halves not yet twisted around 
each other. 
Fig. 20. Various shapes of bivalent chromosomes. 
Fig. 21. A typical bipolar spindle showing metaphase. The cell-wall is very thick. 
