CYANOPHYCE^. 89 



the escape of the contents of a small diatom escaping from 

 the valve, increasing by growth and secreting a new wall. 

 Sometimes two auxospores formed by the same mother-cell 

 coalesce to form a new individual ; in others the two 

 auxospores produced by a single mother-cell form distinct 

 individuals after growing to the normal size. The third 

 method is by the conjugation of two distinct individuals, 

 which become arranged side by side ; the contents of the two 

 escape by the opening of the valves and combine to form a 

 zygospore. This latter method, although closely resembling 

 tTie process of conjugation acknowledged as a sexual act in 

 some of the higher algae, as Sfirogyra, etc., is not considered 

 by some of the best authorities as a true process of sexual 

 conjugation in the present instance. The above described 

 modes of reproduction are connected by transitional 

 methods. 



Diatoms are aquatic forms met with in both fresh and 

 salt water. Some species are solitary, either free or attached 

 by one side to aquatic plants ; others are attached in clusters 

 by simple or branched gelatinous stalks ; others again occur 

 in immense numbers enclosed in a common gelatinous 

 envelope. The Diatoms, like the Mycetozoa, form a terminal 

 group. 



Cyanophycese. 



The leading feature of the present group is the presence 

 of a blue-green colouring matter dissolved in the cell-sap, 

 and consequently masking the green colour of the chloro- 

 phyll, which is always present. The most general mode of 

 reproduction is by fission or cell-division ; thick-walled 

 resting-spores are formed' in some cases, and in the higher 

 filamentous forms short portions of the filament known as 



