222 SEMI-CENTENNIAL OF TORREY BOTANICAL CLUB 
fixed in the colonies of Pediastrum. It is possible that the six- 
teenth cell lies above or below the plane of the colony in this case 
and hence does not appear in the photograph. Оп the other 
hand, it may be that cell a did not undergo the third division and 
has remained larger than its fellows. 
Fic. іі. Pediastrum simplex Meyen.  Fifteen-celled деви: one cell, a, larger 
than the others; bristles and pear-shaped basal bodies show on some of the spines 
in the original, but are practically lost in reproduction. ЖХ about 
Nitardy ("14, p. 183) figures a specimen of P. Boryanum with 
fifteen cells, one of which is much larger than the others and 
contains a double pyrenoid. There is also a faint line running 
across the middle of the cell and Nitardy is convinced that the 
large cell has arisen by fusion of two swarm-spores. He notes 
that this is the only case of anomaly in cell number which he has 
observed in twenty years of study of the group. It would seem 
that the large cell might equally well be due to a failure of one of 
the cells to complete the third division. The larger size of the 
cells in the sixteen-celled daughter of a thirty-two-celled colony 
C18, FIG. 21) as compared with the thirty-two-celled daughter of 
same mother is conspicuous. 
