SEX AND HEREDITY 



467 



3. The spore-mother-cell has now completely separated from its neigh- 

 bours, and is roughly spherical. The nuclear enlargement noted before is 



FIG. 393- 



Drawing3 by Dr. J. M. Thompson, representing in detail twelve successive stages 

 in the tetrad-division of the pollen-mother-cell of Allium Ursinum. ( x 1000.) For 

 the detailed description see Text. 



maintained, but the linin-reticulum is resolved into a definite number (in this 

 case sixteen) of slender chromosomes. A nucleolus is still recognisable. 



