SFX IN UNICFI.LULAR ALGAE 117 



them; Pringshcini and Ondratschck (1939) consider rlieir arrest of 

 motility an important corollary of chemotaxis. 



In species where both gametes remain actively motile, however, 

 a chemotactic mechanism Mould seem to be virtually useless. None 

 has been observed in Cbhrinydovionas vioewiisiiy for example (Ilutner 

 and Provasoh, 1951). In C. eugametos Moewus (1933) found no 

 evidence for chemotaxis when gametes of one mating type were 

 allo\\ed to swim near the mouth of a capillary tube filled with filtrate 

 from cells of the opposite mating type, or near cotton or agar soaked 

 in such a filtrate. Some years later (1939b) the same author reported 

 in this species positive chemotactic responses to gentiobiose and iden- 

 tified the naturally occurring tactic agents with the gamones, viz., 

 proportional mixtures of cis- and trans-d^imtxhyX crocetin. His earlier 

 failure to demonstrate such agents he explained (1941) by the 

 fact that he had not at first appreciated the photolability of the sub- 

 stances concerned. 



Clumping 



When active gamete suspensions of C. inoenjoiisii are mixed, the 

 cells seem to show no appreciable change in behavior until, by ran- 

 dom contact, flagella attached to cells of complementary mating type 

 make contact and adhere (Gerloff, 1940; Lewin, 1952b). As in C. 

 eugauietos (Moewus, 1933), large clumps of 100 or more cells may 

 be quickly built up in dense suspensions, whereas in sparser cultures 

 the cells associate in smaller groups of as few as two or three cells. 

 Such clumps were first described by Berthold (1881) in gametes of 

 Ectocarpiis, and have been since observed in a wide variety of other 

 algae with motile gametes. Non-swimming (ultraviolet induced) 

 mutants of C. moenjousii (Lewin, 1952a) mate comparatively poorly 

 with normal swimming cells, as might be expected. In paralyzed 

 stocks of the homothallic C. dysosmos, or in mixtures of C. moeuousii 

 in which cells of both mating types are unable to swim, virtually no 

 mating takes place unless the suspensions are mechanically agitated to 

 bring compatible pairs into contact. 



In Tetraspora (Geitler, 1931) and C. inoeixnisii (Hutner and 

 Provasoh, 1951), clumping has been observed between cells killed 

 by gentle heating, ultraviolet irradiation or other treatments, and 

 living cells of the complementary mating type. 



