334 EXPLANATION OF THE PLATES. 



PLATE IV. 



Pediastrum granulatum, Kg. 



(Continued from?^. III.) 



Fig. 1, Disk of eight cells, placed 1+7, derived from 

 the same mother-disk as the four-celled disk represented 

 in fig. 11, of PI. 3. 



Fig. 2. Full-grown eight-celled disk, l-f7. The con- 

 tents of the cells dark green, and granular; the starch- 

 grains no longer visible. The cell-walls in the interior 

 of the disk are tinged slightly crimson, which colour, 

 however, only occurs sometimes in full-grown specimens. 



Fig. 3. Eight-celled disk arranged 1+6+1, a very 

 rare exceptional case. 



Fig. 4. Disk in 1+5+10, which is the most frequent 

 case with sixteen cells, (see fig. 5, PI. III.) 



Fig. 5. Disk of sixteen cells, 6+10, the inner six 

 differently arranged from those of fig. 7, PI. III. 



Fig. 6. A similar one, but the outer circle so closely 

 adjoined to the inner that the arrangement appears 

 spiral. 



Fig. 7. Abnormal disk of fifteen cells, in which, how- 

 ever, one in the outer circle is larger than the rest, and 

 doubtless stands in the place of two, from omission of the 

 last division in the formation of gonidia. The likewise 

 irregular arrangement may, therefore, be regarded as 

 5+10+1. 



Fig. 8. Elliptical disk of sixteen cells, 5+10. 



Fig. 9. A similar disk, but the five inner cells in a 

 different position. 



Fig. 10. Elliptical disk of thirty-two cells, 7+11+14. 

 The colonies of thirty-two cells are rarer in this species 



