SEXUALITY 



675 



intensity 3, to K with intensity 2, to J with intensity 1, and not at all 

 to H. Moreover, the weak reaction of G with J is not due to the weak- 

 ness of J, for J reacts with intensity 3 in mixture with L, while the latter 

 gives but a weak reaction with N. Consequently the strength of the reac- 

 tion is not a general characteristic of a given sex, but depends in some 

 way on the particular combination of sexes. When the sexes are arranged 

 as in Tables 8 and 9, the differing intensities of reaction fall into a defi- 

 nite system: the strength of reaction between sexes increases with their 



Table 9: Grades of Sex Reaction in Mixtures of Sexes G to O from 



THE Chlmnydomonas species C. hraunii, C. dresdeusis, and C. 



eugametos (forms typica, simplex, subheteroica, 



AND SYNOICA) 



* Mixtures made from cultures with cells in concentration of 2 x 10" per cc. O = no reaction ; 

 1 = pairs only; 2 = clumps of 10 to 20 cells; 3 = clumps of 100 or more cells. Data from Moewus, 

 1938a. The designations of the sexes differ from those used by Moewus. 



distance apart in the table until the maximum reaction (grade 3) is 

 reached. These quantitative differences in intensity of sex reaction sug- 

 gest that the fundamental differences among the sexes are also quantita- 

 tive, a suggestion strikingly confirmed by studies of Moewus on the 

 chemical basis of the sex reaction, as will now be set forth. 



The culture fluid in which ripe gametes are living has been shown, 

 in a number of algae, to contain material ("sex stuffs") capable of af- 

 fecting the sexual behavior of other gametes. In Chlamydomonas, 

 Moewus (1933, and later) obtained this material free from the or- 



