THE PROBLEM OF SEX IN PLANTS 355 



plant of one strain grows next to a plant of another 

 strain, conjugation will always take place between them. 

 These strains he designated, provisionally as (+) and ( ) 

 (Fig. 190). The (+) strain is vegetatively more vigorous 



FIG. 263. Spirogyra sp., illustrating sexual differentiation. Receiving 

 (female) gamete at the left; supplying (male) gamete at the right. (Re- 

 drawn from camera lucida drawing by H. H. York.) 



than the ( ) strain, and the conclusion seems warranted 

 that the (+) race is female and the ( ) race male. 



322. Sexual Differentiation of Spores. i. Physiolog- 

 ical. Even an elementary study of reproduction reveals 

 the fact that spores from the same plant, and even from 

 the same sporangium (as in some of the molds just men- 



