344 BOTANICAL GAZETTE [october 



range of varying conditions; (6) the sex act results in a zygote 

 which is formed under conditions unfavorable to vegetative activity, 

 and therefore passes into a protected dormant condition; in other 

 words, the conditions which favor the formation of a zygote inhibit 

 its germination; (7) a zygote may function as an ordinary spore, 

 producing a new individual, or it may produce spores, functioning 

 like an ordinary protoplast; (8) the physiological changes involved 

 by the introduction of the sex act are very great and far-reaching, 

 for they include the mutual attraction of gametes, the organi- 

 zation into a single cell of the contributions of two cells, a provision 

 for reducing the number of chromosomes which the sexual fusion 

 has doubled, and the appearance of two kinds of individuals pro- 

 duced by spores and zygotes. 



The differentiation of sex 



The differentiation of sex usually discussed is morphological 

 differentiation, which means in this case a visible difference in the 

 size and activity of gametes, so that they can be recognized as male 

 and female. The increase in bulk of one of the pairing gametes is 

 observed to be due chiefly to the increased bulk of cytoplasm, and 

 on this account the egg is said to have much greater nutritive 

 capacity than its mate. This is probably not the only function of 

 the cytoplasm of the egg in connection with the sex act, but what- 

 ever the functions may include, they are evidently as subsidiary 

 to the act as are swimming appendages and mutually attractive 



substances. 



gamete 



ance is the sperm, and its variability has to do chiefly with its swim- 

 ming appendages, its form, and its amount of cytoplasm. From 

 algae to gymnosperms, the apparatus for locomotion is developed 

 in a variety of ways, reaching a high degree of specialization in such 

 groups as the ferns and cycads. But among the angiosperms and 

 higher gymnosperms a very different situation has developed, for 

 motility has disappeared, even in its simplest expression. It 

 follows that all the elaborate specialization of the sperm of ferns 

 and cycads has to do with their motility, and not at all with their 

 function as gametes. It is evident also that even the simple cilia 



