physiology; symbiosis 417 



demonstrated for Dasycladus clavaeformis^ Tetraspora luhricuj 

 Sphaeroplea, Chlamydomonas eugametos, Protosiphon botryoides, 

 Stephanosphaera pluvialis and Botrydium granulatum (Smith, 

 1 951). A story has apparently been worked out for Chlamydomonas 

 eugametos in some detail and this will therefore be discussed. 



Chlamydomonas eugametos when grown on agar Uves in the palm- 

 elloid state. When flooded with water and irradiated with light 

 flagellae are first formed, then the cells become motile, and, if the 

 irradiation is continued, sex determination takes place followed by 

 copulation, fusion and production of the zygote. These changes are 

 associated with special hormones which can be extracted from the 

 filtrate at the different stages in the process. These hormones are 

 present in such small quantities that 200 litres of rich filtrate are 

 required and analysis even then must be spectroscopic. The se- 

 quence of events is illustrated in Table 22(a) which also indicates 

 the nature of the sex hormones. The hormone responsible for pro- 

 duction of flagellae has been identified as crocin. The hormones 

 that actually determine the sex of the gamete are called termones, 

 those that determine the female being gynotermones and those de- 

 termining the male androtermones. There appear to be two of each 

 in C. eugametos. In addition the substances responsible for attrac- 

 tion between male and female gametes are termed gamones. It is 

 likely that the gamones are produced by the flagellar sheath since 

 the sheaths appear to be responsible for agglutination. These have 

 been identified as cis- and trans-crocetin dimethyl ester. When cis- 

 is in excess the mixture is a gynogamone and when the trans- is in 

 excess the mixture is an androgamone. It has further been suggested 

 that the degree of relative sexuality in C. eugametos and species 

 interfertile with it depends on the relative proportions of cis- and 

 trans-crocetin dimethyl ester. The intensity of sexuality between 

 male and female gametes has been termed the valency and the 

 relation of valency to the cis-/trans- ratio is shown in Table 23. 



Table 23 



Proportions of cis- and trans-crocetin dimethyl ester in male 

 and female gametes of different valence in Chlamydomonas 



eugametos {after Moewus) 



Valence $5 ?4 ?3 ?2 ?i c?i c?2 c?3 c?4 c?5 

 '''ratio''' 98-2/r8 95/5 85/15 75/25 65/35 35/65 25/75 15/85 5/95 I-8/98-2 



