Feb., 1922 sexual evolution in the plant kingdom 113 



microsporocytes give rise to four microspores, as the result of 

 reduction, and all of the four develop into male gametophytes. 

 The reduction division in this case as in others segregates the 

 chromosomes with their complements of Mendelian factors, 

 but sexuality is not involved in such segregation and is not 

 affected or changed by it. It is, therefore, self evident that 

 fundamental sexual phenomena are caused by properties in 

 plants entirely apart from Mendelian units. 



The specific structures and functions developed in the 

 ontogeny of an organism appear to be conditioned on the inter- 

 action of four fundamental influences: (1) the hereditary fac- 

 tors themselves, apparently properties of the chromosomes; 



(2) the influence of the environment, both external and internal; 



(3) the progression of senility, probably including a fundamental 

 exhaustion and degeneration of the protoplast as well as 

 retardation or change of its activities due to chemical deposits; 

 and (4) the presence of sexual states in the living substance, 

 through which primary and secondary sexual characters and 

 functions are produced and which are probably positive and 

 negative states of atoms or molecules contained in the living cell. 



