EUPHYCOPHYTA 23 



Carteria ovata (cf. also p. 427), but it has now been demonstrated 

 that the two species represent the haploid and diploid somatic 

 phases respectively of one species. Whether these examples repre- 

 sent a true alternation of generations or whether they must be 

 regarded as possessing a special type of zygote will be considered 

 later (seep. 312). 



The genus is widespread, the various species occurring prin- 

 cipally in small bodies of water, in sewage oxidation lakes (see p. 

 453) and in the soil. 



Within the family Chlamydomonadaceae there is a considerable 

 variety of forms. Among those which lack a true cell wall is the 

 pear-shaped, 4-ciHate Polyhlepharides and the biciliate Dunaliella. 

 In Phacotus the chlamydomonad cell is surrounded by a special 

 outsize hardened envelope which is flattened in side view. Polytoma 

 is a colourless member of the family but nevertheless produces 

 starch as its food reserve. 



* Sphaerellaceae : Sphaerella (sphaer, ball; ella, diminutive of 

 affection). Fig. 3 



B 



Fig. 3 Sphaerella lacustris {Haematococcus pluvialis). A, diagram 

 of single macrozoid. b = blepharoplast, c = chloroplast, ct =flagelluin 

 tube, cw =cell wall, n = nucleus, nu = nucleolus, p =pyrenoid, ps = 

 protoplasmic strand, r = rhizoplast, 5= stigma. B, encysted plant 

 with haematochrome in centre. C, eight-celled palmelloid stage. 

 D, diagram Illustrating life cycle in bacteria-free cultures. (After 



Elliott.) 



