PROTOPHYTA 



57 



In all cases the fusion of the gametes in this group is com- 

 plete, resulting in a zygote* which may become a zygospore by 

 developing a resistant membrane which is frequently ornamented 

 with short spiny processes. 



The motile phase is dominant in all of the above forms, the 

 jelly-invested or palmella stages being transient or absent alto- 

 gether. In other related groups, however, the motile stages are 

 of short duration and the palmella stage is the dominant form. 

 The type genus here is Palmella, in which form the individuals 

 are minute green cells surrounded by gelatinous coatings which 

 fuse into a homogeneous matrix — hence the term "palmella 

 phase" as applied to other organisms. In some cases the cells 

 fuse in the form of long gelatinous rods; in other cases in groups 

 of four cells. Zoospores, or flagellated individuals, and iso- 

 gamous gametes are known in practically all types. 



Group Chlorococcales 



In many of the simpler and non-colony-forming types of the 

 Volvox group, the flagella are withdrawn during the process of 

 cell division. If such a transient, motionless stage should be 



Fig. 28— GON1UM PECTORALE 



A common form of colonial fresh-water plant flagellate. Left, an 

 ordinary vegetative colony; right, the same in reproduction; each indi- 

 vidual of the ordinary colony forms a sixteen-cell colony 



From photomicrographs by the author 

 Magnification, 400 



extended for long periods, there would result a type with the main 

 characteristics of the group Chlorococcales. In this type, the 

 solitary individual loses its flagella and grows to a certain size, 



* Zygote, a fertilized cell. 



