PROTOCOCCOIDE.E. 93 



a naked cell or become enclosed in a very thin cellulose 

 wall, furnished with openings through which the cilia 

 protrude. In some instances the protoplasm of the passive 

 cell, instead of escaping as a single large zoospore, breaks 

 up before escaping into several small zoospores. After 

 existing for some time in an active state, the cilia contract 

 into the mass of protoplasm, which secretes a thick cell-wall 

 of cellulose, and returns to the palmella stage as a resting- 

 spore, which possesses the power of retaining its vitality for 

 years in the form of dry powder, and may be carried for a 

 considerable distance by the wind and at once resume their 

 vitality when placed in water. The power of assimilating 

 carbonic dioxide and liberating oxygen under the influence 

 of light, as also the secretion of a cell-wall composed of 

 cellulose, prove the plant nature of Protococcus. In some 

 genera, as Chlorothecium, swarm-spores are produced which 

 conjugate by the gradual fusion of two such bodies into one, 

 which may be considered as the earliest indication of sexual 

 reproduction amongst the chlorophyll-producing forms of 

 plant life. 



As in the Cyanophyceae, many forms at present included 

 in the present group may ultimately be shown to be 

 conditions of higher AlgK. 



Commencing with the Alg» proper, we may be considered 

 as clear of debatable ground, and dealing with organisms 

 where those differentiations considered characteristic of 

 plant life are distinctly evolved. 



The following diagram illustrates the divergence of the 

 groups already mentioned from the primitive Flagellate 

 Infusoria. 



