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SUMMARY Gas‐liquid chromatography of algal extracts provides a sensitive assay for their content of 1‐(O‐α‐d‐glycopyranosyl)‐3, 25‐hexacosanediol, the principal glycolipid from the envelope of heterocysts of Anabaena cylindrica. Different patterns of lipids were found in the heterocysts of 5 species of Anabaena and Nostoc. Lipids with comparable chromatographic properties were detected in Gloeocapsa.

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Male and female mating types of Chlamydomonas eugametosMoewus show an absolute light requirement for gametogenesis. Increasing light intensity from 0.3 to 1.2 mw cm-2 during nitrogen starvation (a precondition for gametogenesis) caused an increase in gametogenesis throughout a 28-hour period. Gametogenesis was measured by determining the percentage of paired cells after a 1-hour mixing period. Light requirements for the male and female differed. There was a 9-hour lag period in gametogenesis in the male, but no lag in the female. Gametogenesis was reduced 50% in the female and 90% in the male when 6.0 AM 3-(3,4-dichlorophenyl)-1, -dimethylurea was in the N-starvation medium. Sodium acetate, 1.8 mM, in the N-starvation medium increased gametogenesis in both mating types and eliminated the 9-hour lag in the male for cells irradiated for 3, 6, 9, 12, 15, 18, or 23 hours during the last part of a 23-hour N-starvation period. Sodium acetate concentrations higher than 1.8 mM inhibited the mating process. 3-(3,4-Dichlorophenyl)-1,1-dimethylurea inhibition of gametogenesis was decreased in the male but increased in the female, when sodium acetate was added to the N-starvation medium. These results indicate a nonphotosynthetic as well as a photosynthetic role for light in the gametogenesis of both mating types. Also, the male will not undergo gametogenesis unless a required amount of energy is provided either in the medium or through photosynthesis.Chlamydomonas eugametos Moewus was first described in 1931 (13). Moewus (14-16) conducted much of the early work on its life cycle and differentiation from vegetative cell to gamete. There are two morphologically undifferentiated mating types of C. eugametos. The male carries out the locomotion of the mated pair (8,23).The mating process in Chlamydomonas occurs in a strictly ordered fashion (2, 10). Gametogenesis, the physiological differentiation of male and female vegetative cells into gametes, (5) also stated that the female did not require light for sexual activation. These observations on the light requirement, or lack thereof, were again made in later works (3, 4). These findings contradicted the earlier work of Moewus (14, 15). He found there were definite light requirements for both the male and female, and that light was still required even when the cells were N-starved in a 1 % sugar solution. Sager and Granick (17) reported that light was required for conversion of both types of vegetative cells of C. reinhardi to gametes. Lewin (11), studying control of sexual activation in C. moewusii Gerloff by light, noted that both types required light, and that this light requirement could not be replaced by the addition of any chemical or natural extracts of the medium. In the current study, the reasons for these differences are resolved. MATERIALS AND METHODSMedia and Growth Conditions. Strains 9 (male) and 10 (female) of Chlamydomonas eugametos Moewus were obtained from the Indiana Culture Collection (18). Cells were grown and maintained on agar slants at 25 ± 2 C...