CHRYSOPHYCOPHYTA 273 



Taxonomy 

 Hustedtj F. (1930). Die Kieselalgen. In Rabenhorst's Kryptogamen- 

 Flora von Deutschland, Oesterreich und der Schweiz. Vol. 7. 

 Leipzig. 



Melosira 



Stosch, H. A. von (1950). Nature (Lond.), 165, 531. 



Chrysophyceae 

 Fig. 158 



This assemblage is principally composed of uninucleate flagellate 

 forms although certain members do exhibit some algal character- 

 istics. Like the Xanthophyceae there is considerable morphological 

 paralleHsm with the Chlorophyceae indicating that evolution has 

 taken place along the same Unes. Sexual reproduction is rare and 

 when it does occur is isogamous, the plants probably all being hap- 

 loid. They occur most commonly in both fresh or salt water during 

 cold weather. The colour is golden yellow or brovm due to the 

 presence of the pigment phycochrysin, which is contained in a small 

 number of parietal chromatophores that may also contain pyrenoid- 

 like bodies, although starch as a product of photosynthesis is re- 

 placed by oil or leucosin. The motile cells are uni- or biflagellate, 

 and in the latter event one flagellum is beset with fine ciha; one of 

 the flagella is said to provide forward movement and the other 

 rotation. When an individual has entered the amoeboid state cysts 

 may be produced endogenously and these have siUcified walls com- 

 posed of two equal or unequal parts. The group possesses the 

 following morphological categories : 



(a) Unicellular motile types, e.g. Chromulina. 



\h) Encapsuled types, either free or epiphytic, e.g. Dinohryon 



spp. 



(c) Colonial types, e.g. Synura. 



{d) Dendroid colonies, e.g. Dinohryon spp. 



{e) Rhizopodial or amoeboid types, e.g. Rhizochrysis. 



If) Pahnelloid types, e.g. Phaeocystis and Hydrurus, the latter 

 being a highly differentiated branched type. 



{g) Simple filamentous types, e.g. Phaeothamnion. 



It is suggested that the group is still actively evolving, and that 

 some of the brown types with algal characters may have a relation- 

 ship with the simpler Phaeophyceae. 



