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- 



