1914] COULTER— REPRODUCTION IN PLANTS 347 



what may be called for convenience " sex-determiners" are always 

 present in the plant body. These determiners are conceived of as 

 representing substances that under appropriate conditions react 

 in such a way as to determine the formation and character of the 

 sexual cells. 



Along with sex-determiners there must be sex-inhibitors, for 

 it seems clear that every protoplast contains both determiners, but 

 gamete-forming protoplasts produce only one kind of gamete. It 

 seems probable, therefore, that every gamete-forming protoplast 

 is equipped with two determiners and one inhibitor. 



In the early history of sex the protoplasts of an individual differ 

 as to this equipment, so that the individual is bisexual so far as 

 gamete-formation is concerned. Later, all the protoplasts of an 

 individual are alike in sexual equipment, and as a consequence 

 individuals are sexually differentiated. Finally, with the appear- 

 ance of heterospory, sexual individuals are permanently differ- 

 entiated. 



Apparently the amount of available nutrition holds no relation 

 to the differentiation of sex, except as it inhibits the production 



small 



same time 



sperms. In other 



determine sex, but sometimes 



the opportunity for the expression of sex. 



All the sporophytes contain both sex-determiners, and in sporo- 

 genesis they are transmitted to the spores, which may produce 

 bisexual gametophytes or unisexual gametophytes, dependent 



upon the distribution of the inhibitors. 



All fertilized eggs contain both sex-determiners and inhibitors, 

 and may transmit them all to the sporophyte, in which case the 

 sporophyte would produce spores functioning alike, or two kinds of 

 spores differing in their inhibitors. 



In the case of the monosporangiate sporophyte of seed plants, 

 the fertilized egg transmits to the sporophyte only one inhibitor, 

 which determines whether it produces megaspores or microspores. 



The presence of sex-determiners and inhibitors determines not 

 only the character of the gametes produced, but also the character 

 of the sexual structures associated with them; and, in the case of 



