10 THE ALGAE 



and the development of short algal filaments, e.g. Dinothrix^ Dino- 

 clonium (cf. p. 277). Many are surrounded by a cellulose wall bearing 

 elaborate sculptured plates. Inside the cells there are dark yellow 

 or brown discoid chromatophores which contain a number of 

 xanthophylls not so far found in other algal classes. The products 

 of photosynthesis are starch and fat. The motile cells normally 

 possess two furrows, one transverse and one longitudinal, although 

 these may be absent in some of the more primitive members. A 

 transverse flagellum hes in the former, and the latter is the starting 

 point for the second flagellum which points backwards. Sexual 

 reproduction, if it occurs, is isogamous, but it has not been clearly 

 established in the few cases reported. Characteristic resting cysts 

 are also produced by many of the forms. 



Nematophytales 

 (10) Nematophyceae 



This is a fossil group of which one genus has been known for a 

 long time (Nematophyton), whilst the other (Nematothallus) has 

 only been described more recentiy. There is still considerable 

 doubt as to their true affinities, but it would seem that a place can 

 best be found for them as a very highly developed type of alga. 

 Their internal morphology suggests an alhance with more advanced 

 members of either the Chlorophyceae or Phaeophyceae. The only 

 reproduction so far recorded is that of spores which were developed 

 in tetrads. 



REFERENCES 



Fritsch, F. E. (1935). The Structure and Reproduction of the Algae Vol. I, 

 pp. 1-12. Camb. Univ. Press. 



Smith, G. M. (1951). Manual of Phycology, pp. 13-19. Chron. Bot. Co., 

 Walthanij Mass. 



Strain, H. H. (1951). Manual of Phycology, pp. 243-262. Chron. Bot. Co., 

 Waltham, Mass. 



