58 PLANT-LIFE 



gestions we have adduced will be more fully appreci- 

 ated when we come to deal with the Mosses, Ferns, and 

 more advanced alliances. But we have yet to notice 

 an interesting divergent line of development, from a 

 Chlamydomonas origin, which does not involve a Pleuro- 

 coccid stage. 



Gonium pectorale (Fig. 20) is a little plant found on 

 the mud of stagnant pools and ponds. The actual size 

 may be imagined from the fact that our diagram repre- 

 sents the plant magnified 300 

 diameters. It consists of a colony 

 of sixteen adherent cells arranged 

 in the form of a plate, or rosette. 

 Each cell is furnished with a pair 

 of flagella, a red pigment spot, 

 and chlorophyll. The cells are 

 attached to each other by proto- 

 plasmic substance, and the colony 

 FIG. 20. GONIUM PECTOR- * . . J 



ALE. x 300. is invested by a gelatinous mem- 



Colony seen fom flat side, brane, through which the flagella 



a, Nucleus; 6, contractile penetrate on one g i de Q f the plate, 

 vaouole; c, pyrenoid. r . 



The nagella move in unison, as if 

 controlled by a master impulse, and propel the colony 

 through the water. The plant revolves in the water 

 in a wheel-like fashion, and it frequently happens that 

 the observer sees only the edge of the plate. Gonium 

 obeys the command to " multiply and replenish the 

 earth " in two ways. The first mode of reproduction 

 is asexual. All the cells divide simultaneously, there 

 being four successive divisions in each cell, the result 

 being sixteen aggregates of sixteen cells each. These 

 aggregates of newly formed cells break away from the 



