52 



THE ALGAE 



filament is made up of a series of H pieces and as a result the fila- 

 ment readily fragments. At cell division a new H piece is intro- 

 duced between the two daughter protoplasts. In young cells the 

 parietal plastid is commonly reticulate but older cells are so filled 

 with starch that plastid structure is difficult to see. There are no 



D I C 



Fig. 24 Microspora amoena. A, portion of thread. B, early 

 cleavage in swarmer formation. C, two young cells ( x 745). D, 

 akinete formation ( x 550). E, formation of aplanospores. F, G, 

 stages in germination of aplanospores. H, liberation of zoospores. 

 I, zoospores ( x 745). (C, D, I, after Meyer; rest after Fritsch.) 



pyrenoids. Asexual reproduction is by means of biflagellate zoo- 

 spores (quadriflagellate in one species), 1-16 being produced per 

 cell and liberated by the thread fragmenting into H pieces or else 

 by gelatinization of the cell walls. Any cell can produce single 

 aplanospores instead of zoospores, and some species also produce 

 multinucleate, thick-walled akinetes. These germinate directly to 

 form a new filament or with later germination to give four proto- 

 plasts that then grow into new filaments. 



