356 



STRUCTURE AND LIFE HISTORIES 



tioned), and to all external appearances entirely alike, 

 may produce individuals of different sex- value, some being 

 male and some female. 1 Such was also seen to be the 

 case with the marine alga Dictyota? the externally similar 

 male and female gametophytes being produced by spores 

 that are alike in size and other external features. 



As a further advance spores that appear to be morpho- 

 logically alike may produce plants morphologically as well 

 as physiologically different (Anthoceros, some molds). 



2. Structural. In the little club-mosses (Selaginella) 

 we found the spores unlike, not only in function but in 

 structure, those producing males being smaller than those 

 producing females the condition of heterospory. 



FIG. 264. Vaucheria terrestris. anth, antheridium (empty); o, oogonia. 



323. Differentiation of Sex-organs. In many lower 

 plants there is no recognizable structural difference be- 

 tween the organs that produce the heterogametes, but a 

 step in advance in this direction is found in such a plant 

 as Vaucheria (Fig. 264), where the antheridia are struc- 



1 See, also, pp. 246 and 248. 



2 See Chapter XVIII. 



