92 PLANT LIFE. 



Many of the forms at present included in the present 

 group may eventually be shown to be phases in the life- 

 history of higher species of Algae. 



ProtocoocoideBB. 



The organisms included in the present group are all 

 minute, unicellular, never forming long septated filaments, 

 and are characterized by the presence of bright green 

 chlorophyll, which is not masked by colouring matter as in 

 the Diatomacem and the Cyanophycecz. The special interest 

 attaching to the present group consists in the fact that 

 from it all the higher forms of the Vegetable Kingdom have 

 been derived. Some of the species are permanently motile, 

 others always passive, while a considerable number exhibit 

 the two conditions at different periods, as illustrated by 

 Protococcus, a common form in fresh water, where it forms 

 clear green masses of variable size, composed of numerous 

 individuals which consist of a spherical cell furnished with a 

 cell-wall. The green chlorophyll is often mixed with a 

 varying amount of red colouring matter. In this condition 

 the cells are motionless, and reproduce themselves by cell- 

 division. The above quiescent condition is termed the 

 palmella stage. The change to the free-swimming or 

 protococcus stage is accomplished by the protoplasm escaping 

 from the cell-wall furnished with two extremely slender cilia, 

 which along with a pulsating vacuole, enable the organism 

 to move rapidly in the water. The pulsation of the vacuole 

 is said to be due to the action of the chlorophyll in extract- 

 ing carbonic dioxide from the water, and liberating oxygen 

 as a result of assimilation. The motile form may remain as 



