CYANOPHYCE.E 255 



the characteristic form of the filaments of the 

 parent plant. 



Spores are known in certain genera, and probably 

 occur in all. They differ from the ordinary cells in 

 their rounded form, greater size, and more granular 

 contents, and their thick, coloured membrane. On 

 germination the contents shrink from the wall and 

 divide by parallel walls into a number of cells, and 

 this short filament escapes by a perforation or cir- 

 cumscission from the parent membrane. It then 

 becomes practically a hormogonium, and thus repro- 

 duces the plant. In a fresh-water form, Sacconcma, 

 the spore divides by perpendicular walls and gives 

 rise to a globular colony like Glo&ocapsa, but Borzi, who 

 records the observation, did not observe the develop 

 ment of this body into the normal form. 



Homocystece or Oscillariccc. 



General Characters. The characters which dis- 

 tinguish the Hmnocystece from the Heterocystem are 

 mainly negative ; they have no heterocysts and no 

 spores. Their reproduction is solely by hormogonia. 



The Thallus. True branching, as in the Sirosi- 

 phonc-ce, does not occur among the Hamocystecc, and 

 since there are no heterocysts, there is no false 

 branching of the type produced in the Hcterocystcce 

 by the adhesion of the heterocyst to the sheath. 

 Accordingly, in some of the genera the filaments 

 remain simple, but false branching occurs frequently in 

 the tribe Vaginariecc and in Plectoncma (Lyngbycce). 

 The false branching in the former case arises when 



