SEX 373 



to their archegonia, but the male gametophytes could not be made to 

 develop archegonia. In Osmunda regalis japonica and Asplenium nidus, 

 which are monoecious, Nagai (1915) found that the concentration of the 

 Knop's nutrient solution used has a controlling influence over the kind 

 of sex organ appearing, the number of antheridia in general decreasing 

 with the concentration. 



These results, taken together with the fact that many gametophytes, 

 especially those of homosporous pteridophytes, are monoecious, show that 

 the capabilities of both sexes can be present in the haploid nucleus, as 

 Strasburger thought, although in many forms the visibly developed sexes 

 may be automatically determined by some cell mechanism. 



General Discussion. We have now reviewed some of the evidences 

 which have led to two general theories of sex and its determination. One 

 theory represents an attempt to account for the phenomena in question 

 on the basis of a morphological cell mechanism whereby Mendelian or 

 other factors are distributed in a definite and fixed manner, whereas on 

 the other theory it is held that they are the results of a physiological 

 differentiation manifesting itself chiefly in alterable levels of metabolism. 

 Although these two conceptions may appear to be mutually exclusive 

 if expressed in too uncompromising a form, both must contain elements 

 of truth. It is beyond question that the two manifestations of sexual 

 differentiation, the physiological and the morphological, are both of 

 importance and cannot be ultimately irreconcilable: our task is to 

 determine their relative significance and to discover the nature and 

 degree of their mutual interdependence. It seems clear that the digam- 

 etic condition when present in dioecious forms does regulate the ratio 

 of the sexes: under all ordinary circumstances the sex of the individual 

 is here dependent upon the kind of gamete which gives rise to it (or the 

 kind of spore in the case of certain gametophytes). But it is to be 

 emphasized that the dimorphism shown by such gametes or spores is not 

 entirely a morphological one, or even mainly so : in many cases no morpho- 

 logical difference can be detected although the two are clearly different in 

 physiological behavior, as shown by the spores of Phycomyces and 

 certain bryophytes. It is generally inferred that here a structural 

 difference, although invisible, is nevertheless present. 



In this connection it may be recalled that the differences between the 

 male and female gametes, irrespective of any differentiation which may be 

 present among those of either kind, are both physiological and morpho- 

 logical. The primary characters of sex are those possessed by the 

 gametes themselves, and the principal distinction between the male and 

 female gametes seems to be a physiological one which is manifested in 

 their mutual attraction and fusion. Any visible morphological differ- 

 entiations that they may possess are to be regarded as secondary adapta- 

 tions to unlike functions, because of the fact that in many of the lower 



