22 



CHLOROPHYCEAE 



The names of the species and genera do not imply that they 

 provided the actual links in the process of evolution, but that 

 ancestral forms having an appearance similar to that of the examples 

 quoted formed the intermediate stages. The examples are given in 

 order that the student may have something concrete upon which to 

 visualize the scheme. 



As a group the Chlorophyceae are very widespread, occurring in 

 all types of habitat. A few species, e.g. Endoderma, Chlorochytrium, 

 Rhodochytrium, are parasitic, whilst several other species participate 

 in symbiotic associations, e.g. Carteria, Zooxanthella, Chlorococcum 

 (cf. p. 296). 



VOLVOCALES 

 *Chlamydomonadaceae : Chlamydomonas (chlamydo, cloak; monas, 

 single). Fig. 14. 



The ''chlamydomonad" type of cell characteristically possesses 

 a single basin-shaped chloroplast, a red eye, one pyrenoid and two 



Fig. 14. Chlamydomonas. A, B, vegetative individuals of two parents. Az, Bz, 

 zygotes of parents. A x B, fusion between gametes of A and B. ABz, zygote of 

 hybrid. Fi, four hybrid individuals obtained from germination of one hetero- 

 zygote. C, Chlorogonium oogamum, female showing formation of ovum. 

 D, Chlorogonium oogamum, male showing formation of antherozoids. E-G, stages 

 in fusion of C. media ( x 400). H, vegetative division in C. angulosa. I, zygote of 

 C. coccifera. J, conjugation in C. longistigma ( x 400). K, fusion of naked gametes 

 of C. pisiformis ( x 400). L-N, stages in fusion of gametes of C. Braunii. 

 O, fusion of gametes in C. coccifera. P, C. Braunii, palmelloid stage. (A-D, 

 after Fritsch; E-K, after Scott; L-P, after Oltmanns.) 



