Fig. 149 Halosphaera viridis. A, mature cell. B, young cell in opti- 

 cal section. C, mature cell with aplanospores. D, swarmer. (A-C, 

 after Fritsch; D, after Dangeard.) 



Chlorotheciaceae : Characiopsis (like Characium). Fig. 150 



The very name of this genus indicates that it is an analogue to 

 the genus of similar name in the Chlorophyceae. The plants, which 

 are epiphytic, sohtary or gregarious, vary much in shape, even in 

 pure culture, and they develop from a short stalk with a basal 



mucilaginous cushion. The wall, composed of 

 cellulose and pectins, is in two unequal 

 portions, the smaller upper part forming a lid 

 which is detached at swarmer formation whilst 

 in one species the lower part bears internal pro- 

 cesses. Although the young cells are uninucleate 

 and contain one or more chloroplasts, the adult 

 cells are multinucleate containing eight to sixty- 

 four nuclei. Reproduction is either by means 

 of zoospores (eight to sixty-four per cell) or 

 „. ^, . . else by means of thick-walled aplanospores. 



Fig. 150 Characiopsis , . , . . . - ^ . . 



saccata. A, plant. B, which m one species are said to give rise to 

 probable swarmer motile gametes, although this is a feature that 



formation. (After - r t ■ • • 



Fritsch) requires further investigation. 



* Tribonemaceae: Trihonema {tribo, thin; nema, thread). Fig. 151 



This is a filamentous analogue to a form such as Microspora (cf. 

 p. 51) with which it is frequently confused. T. hombycina some- 

 times appears in sheets covering ponds and pools and if these dry 

 up they form an algal *paper'. The unbranched threads are com- 

 posed of cells possessing walls of two equal overlapping halves, with 

 the result that the filaments are open-ended and tend to dissociate 

 into H pieces. At cell division a new H piece arises in the centre 



262 



