SFX IN UNICM.l.UI.AR AKGAF, HI 



white liglu. The reactivation curve does not commence to rise at 

 the origin, but a minimum of V2 to '^^ minutes is necessary before 

 any restoration of sexual activity can be demonstrated. The length of 

 the lag period, the slope of the curve, and the height of the asymp- 

 tote are affected by a variety of factors including intensity and qual- 

 ity of light, temperature, and the length of the preceding period of 

 darkness to which the cells have been subjected. 



Medium 



Attempts have been made by many workers, using different or- 

 ganisms, to evolve media which would specifically elicit or promote 

 sexual activity. \^arious degrees of success have been achieved, and it 

 is not proposed to review the literature on the subject here. In gen- 

 eral, it has been found that dilution of the medium, or transfer of the 

 cells from agar to liquid culture, has a marked effect in promoting 

 gamete formation in a number of diverse algae. Lerche (1937) con- 

 cluded that in Dimaliella the effect was attributable to depletion of 

 nutrients (cf. Klebs, 1896; Schreiber, 1925; Strehlow, 1928-29), since 

 she found sexual activity to increase in aging cultures. In Cylindro- 

 cystis, an apparently homothallic desmid, copulation w^as found to 

 be regularly induced by the depletion of nitrogen in the medium 

 (Pringsheim, 1919). This does not appear to be the case, however, 

 in other algae; for example, Chlauiydoinojias pseudoparadoxa (Moe- 

 wus, 1933), Chlamydobotrys (Behlau, 1935), Tolytoma (Pringsheim 

 and Ondratschek, 1939). In Chlmnydomonas s^)^. (Klebs, 1896; Moe- 

 W'us, 1933; Lewin, 1949a), Brachiomonas (Moewus, 1944), Protosi- 

 phon (Bold, 1933; iMaher, 1946-47) and other genera, the empirical 

 device of flooding agar cultures with water or dilute mineral media 

 has generally been found to be the simplest and most effective method 

 for obtaining suspensions of sexually active cells. 



Schulze (1927) found that gametogenesis in Chlorogoniinn 

 could be induced in 16 to 20 hours at pH values of 7.9 to 10.4. Maher 

 (1946-47) obtained good gamete formation in Protosipbon between 

 pH 4.0 and 9.0 but noted that at the lower values gamete motility 

 was reduced. In Chlamydonwnas inoemusii gamete formation is more 

 active in media of higher pH; pairing takes plac(^ within a pH range 

 of 6.0 to 10.0, being most active between 7.0 and 9.0. In Polytoma, 

 too, pairing was found to be most active at pH 8.0 (Pringsheim and 



