SEXUALITY 679 



5. Every cell has the full Anlagen, or potencies, of both male and 

 female. 



6. These potencies are not localized in any one cell component, but 

 are general properties of all the living material. 



7. The sex manifested by a cell is the result of a weakening or 

 strengthening of the expression of either the male or female potency. 



8. This weakening or strengthening may be determined by outer 

 conditions, or by developmental conditions, or by genetic factors. 



9. The degree of weakening or strengthening depends upon the ef- 

 fectiveness of the determiners listed in proposition 8. 



10. This quantitative variation results in the appearance of each sex 

 in a series of strengths called valences. 



11. Sexual union takes place only under one or the other of two 

 conditions: (a) when the gametes diifer in sex; i.e., when one manifests 

 a stronger male than female potency, the other a stronger female than 

 male potency; (b) when the gametes are alike in sex, but very different 

 in sex valence; e.g., when one is strong female, the other weak female; 

 or when one is strong male, the other weak male. 



12. Sexual union equalizes or reduces the tension resulting from dif- 

 ference in sex or sex valence. 



The work on Chlamydomonas shows that physiological sex differences 

 may exist in cases in which morphological sex differences are lacking. 

 This is most clearly evident in those species and races in which each 

 clone consists exclusively of one sex type. Here sexual union takes place 

 only between gametes from different clones, the physiological sex dif- 

 ference of which has been demonstrated. Moewus and Hartmann fur- 

 ther hold that similar physiological sex differences distinguish the unit- 

 ing gametes in species and races manifesting copulation among the 

 members of a single clone. The evidence for this, drawn from experiments 

 employing the "left-over" technique, has been set forth on pages 670- 

 671, along with the contrary evidence of Pascher and of Prings- 

 heim and Ondracek. There thus remains some doubt, even within the 

 genus Chlamydomonas, as to whether sex union is invariably accom- 

 panied by sex differences. 



Hartmann's contention that sex differences are always male and fe- 

 male could not at first be applied to Chlamydomonas. Moewus, there- 

 fore, simply classified the sexes as plus (-|-) and minus ( — ). In the 



