i8 



THE ALGAE 



consists of 9-1 1 separate fibrils arranged in a ring. It is possible 

 that this structure is general throughout the class. In the light of 

 recent electron-microscope studies of the flagella of brown algae 

 (cf p. 125) and of Chlamydomonas (p. 21), it is possible that the 

 structure of all of these will prove generally similar. In the motile 

 forms the flagella are associated with other structures which are 

 collectively known as the neuromotor apparatus. At the base of 

 each flagellum is a granular hlepharoplast. These are connected by 

 a transverse fibre^ or paradesmose, and this or one of the blepharo- 

 plasts is also connected to the intranuclear centrosome by a thin 

 strand called the rhizoplast. The motile cells also possess a red eye- 

 spotj the detailed structure of which is not yet elucidated in all the 

 groups, although it appears to contain a primitive lens in the Vol- 

 vocales. The mechanism is regarded as consisting of two parts: a 

 light absorber near the flagellum base and a shading organ. Two or 

 perhaps three red colouring pigments are sometimes present and 

 are said to be due, at least in part, to the chromolipoid pigment 

 haematochrome (cf. Fig. i). 



Fig. I Aj diagram of eye-spot of Chlamydomonas. p = pigment cup, 

 5=photosynthetic substance. B, diagram of cross-section of eye- 

 spot of Volvox. L =lens, p = pigment cup, s = photosynthetic sub- 

 stance. C, aplanospores of Microspora willeana ( x 600). D, 

 akinete of Pithophora oedogonia ( x 225). (After Smith.) 



Vegetative reproduction takes place through fragmentation and 

 ordinary cell division, though in the Chlorococcales and Siphon- 

 ales cell division is unknown. Asexual reproduction is by means of 

 bi- or quadriflagellate zoospores, except in the Oedogoniales where 



