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- 
