122 SEX IN MICROORGANISMS 



is some evidence that in Chlaiuydoinonas the wavelengths of light 

 concerned are those absorbed by the chloroplast, so that the energy 

 for cell fusion may be provided indirectly by photosynthesis. 

 The flagella are not normally shed (as stated by Gerloff, 1940: cf. 

 C. tipsaliensis; Skuja, 1949) but can be seen to be withdrawn or re- 

 sorbed, as in Tetraspora (Klyver, 1929), in Protosiphon (Bold, 1933), 

 and in C. engametos indica (Mitra, 1951) and C. chlaviydogama 

 (Bold, 1949), in the course of about 30 minutes. Half an hour later 

 the cells finally fuse, the actual fusion taking place quite rapidly in 

 this as in other species of Chlamydomonas. 



The fate of the chloroplasts is usually unknown, though in Phyl- 

 lovwTias (Korschikoff, 1926) they are said to fuse. A study of the 

 genetics of plastogene mutants in such algae would undoubtedly 

 provide valuable information on this point. 



In Chlorogoiihnn oogavnnn (Pascher, 1931) and Carteria iyejj- 

 garii (Ramanathan, 1942) the egg cells shed their walls before fertili- 

 zation. In those species where the gametic cells are furnished with a 

 cell wall, the statement has occasionally been made that the walls 

 themselves coalesce in cytogamy (for example, Chlamydomonas 

 brainiii, Goroschankin, 1890; C. eiigametos, Moewus, 1933; C. en- 

 gametos indica, Mitra, 1951; C. ///oeivusii, Gerloff, 1940; C. upsalien- 

 sis, Skuja, 1949); but it seems most likely that in all species with 

 walled gametes — as described in C. media (Klebs, 1896), C. 

 elongata,. (Korschikoff, 1923), C. panpera (Pascher, 1931-32), C. g}'?;/- 

 7iogy7je (Pascher, 1943), C. chlamydogama (Bold, 1949), and C. moe- 

 iV7isii (Lewin, 1952c) — the walls are actually shed before (Smith, 

 1950b) or during cytogamy. In C. moenxmsii and other species of 

 ChlafJiydomonas the fusing gamete protoplasts become invested in a 

 primary zygote membrane of characteristic staining properties 

 (Lewin, 1952c), and the formation of such a membrane appears to 

 be a common phenomenon among related algae. 



The DiPLom Zygospore 



Fusion of the nuclei is usually difficult to follow: in Chlamydo- 

 botrys and Protosiphon caryogamy may take place about 4 hours 

 after copulation (Strehlow, 1928-29; Bold, 1933). Meanwhile, within 

 the primary membrane, the zygote secretes a thick, highly imper- 

 meable wall, often characteristically patterned in relief (in Brachio- 



