McAllister—Cytology and Embryology. 
635 
The spirem segments formed by the transverse segmentation 
continue to shorten and thicken (Fig. 23). The central knot 
becomes looser and finally the chromosomes become separated 
out of the mass and we have the diakinesis stage (Figs. 24 
and 25). 
It will be seen from the preceding description and figures 
that there is nothing in the prophases of the heterotypic division 
of the pollen mother cells of Smilacina racemosa which suggests 
the approximation of the two limbs of a spirem loop to form a 
double heterotypic chromosome. Such a process could not pos¬ 
sibly be fitted into the series shown in figures 17 to 25. 
Neither is there at any stage a sudden doubling of the thickness 
of the spirem, as would necessarily be the case if there were an 
approximation of the two limbs of a loop to form a heterotypic 
chromosome. The increase in the thickness of the spirem be¬ 
fore and after transverse segmentation is gradual throughout 
the prophases. All possibility of the end to end pairing of two 
somatic chromosomes with a subsequent bending upon them¬ 
selves and approximation to form the double heterotypic chromo¬ 
somes is thus excluded in the heterotypic prophases of Smila¬ 
cina racemosa. 
Strasburger (98) has held that this second contraction phase 
is brought about by a grouping of the individual loops around 
the nucleolus. He suggests that some nutritive relation may 
exist by which the nucleolar material is added to the spirem. 
He believes that the presence of more than one nucleolus will 
cause a corresponding number of centers about which the spirem 
will mass or there may not be any massing at all. 
Fig. T9 show that the central massing of the spirem may oc¬ 
cur with nucleoli outside of the contraction figure. This is 
generally true in S. racemosa in which, as above noted, several 
nucleoli may be present. Although nucleoli may at times be 
included in the central mass it is clear that no relation here ex¬ 
ists between the number and position of the nucleoli and the lo¬ 
cation of the central contracted spirem tangle. In no case did 
I find auy appearance that could be interpreted as showing sev- 
