ioiq] STOUT—JXTERSEXES 127 



capable of fusion when juxtaposed. It may consist of (i) the 

 more or less immediate modification of physical structure of the 

 cells (in spermatogenesis and oogenesis) that are to fuse, and 

 (2) of modifications of organs associated with the development 

 of sex cells, either in the sporophyte or the gametophyte, or both. 

 All of these latter are in reality secondary sex characters; true 

 primary sex characters are to be considered as belonging to the 

 cells that fuse, a view clearly stated by Strasburger (26). 



The relationship between morphological and physiological sex 

 differentiation is well shown in the flowering plants. We may 

 take a hermaphrodite with perfect flowers as a type. Primarily 

 such a plant is a spore-producing individual; it is a sporophyte 

 in which heterospory is in evidence. The stamens bear micro- 

 spores, the pistils bear macrospores. These spores are asexual 

 in that they are not able to fuse. They are sexual, however, to 

 the extent that sex is here already determined. Anatomical 

 expression of maleness and femaleness here appears in sporophytic 

 structures, and the particular sex of the future generations of 

 cells in asexual descent is predetermined until the next fusion of 

 sex cells or the development of a sporophyte through apogamy^ 

 The pollen grains grow into microgametophytes producing male 

 sex cells or sperms. The macrospores grow into the macro- 

 gametophytes which produce the eggs. The alternation of gen- 

 erations is marked; the one is sporophytic; the other is 

 gametophytic. But maleness can be traced back through the 

 pollen tube, through pollen, beyond reduction divisions, to the be- 

 ginning of somatic differentiation of stamens. Likewise femaleness 

 can be traced to the beginning of the organogenesis of the pistil. 

 These facts certainly justify the application of the terms male and 

 female to structures that in their morphology are sporophytic. 

 This view has frequently been criticized by those who emphasize 

 the morphology of the alternation of generations (MacMillan 20). 

 Furthermore, it is to be noted that in the greater number of ani- 

 mals the gametophytic generation is omitted or perhaps to be con- 

 sidered as reduced to a single cell generation, and that here the 

 conditions of maleness and femaleness are most essentially proper- 

 ties of individuals and structures that are wholly sporophytic. 



