May, 1919] Nature of Diecious Conditioyi 415 



activity and latency of the factors that control the development 

 of sexual gametes or organs, or other sexual peculiarities pos- 

 sessed by the organism. 



An examination of the Hfe cycle of one of the higher plants, 

 like Selaginella kraussiana (Kunze), shows that sexuality as 

 expressed in the male and female gametophytes, or as slightly 

 indicated in the microsporophylls and megasporophylls of the 

 sporophyte, is not Mendelian and cannot have any relation 

 whatever, primarily, to Mendelian factors, or Mendelian 

 combinations and segregations; for the simple reason that 

 the beginning of sexual differentiation is initiated in the tissues 

 of the mature sporophyte. Furthermore, when the reduction 

 division occurs in which the synaptic chrosomes are segregated 

 and with them the possible Mendehan factors the four mega- 

 spores or the four microspores resulting are not half of one sex 

 tendency and half of the other, but all of the four spores result- 

 ing from a reduction division are of the same sexual state and 

 all four give rise to females or all four to males, depending on 

 which sexual state was established in the tissue from which the 

 sporocyte originated. Again, after the gametophytes have 

 . developed and matured their gametes, the resulting zygote is 

 not determined as male or female, or more properly speaking 

 as microsporangiate or megasporangiate, but the resulting 

 sporophyte is neutral until it begins to form its strobili when 

 both male and female expression originate side by side in its 

 vegetative tissues as stated above. It is simply impossible to 

 think of a Mendelian formula for the sexual expression of. such 

 plants when the ontogenetic processes do not permit combina- 

 tions and segregations of sex-determining factors to take place 

 in the chromosomes. In consequence of the above facts it 

 comes about that in this species of Selaginella the proportion 

 between the sexes of the gametophyte generation is about 1 

 female to 5,000 males instead of about 1 to 1, as would follow 

 if sexuality were controlled by factors segregated in the reduction 

 division. 



This conclusion has been evident to the writer ever since 

 he began to plot the life cycles of plants as an aid to teaching 

 in general botany. In the first edition of his "Laboratory 

 Outlines for the Elementary Study of Plant Structures and 

 Functions from the Standpoint of Evolution"* the following 

 statement is made: "Male or female sex is not an inherited 



' Journal of Applied Microscopy and Laboratory Methods, 5 : 2056. 1902. 



