SEX DETERMINATION 213 



intermediate stage between i and 3 is probably seen in heterosporic 

 ferns. 



1 . Bisexual Gamophase 



The first type of sex determination is essentially non-genetic and 

 therefore does not concern us here. One must imagine that the possi- 

 bilities of producing male or female gametes are present in all the 

 gamophase organisms of this type; and the potency of the gametes may 

 be subject to variation as in Ectocarpus. The determination of which 

 type of gamete is actually developed is performed by environmental or 

 developmental conditions. 



2. Separately Sexed Gamophase 



The second type of sex determination is found in many lower plants. 

 Marchal,^ working with dioecious mosses, was able to show very clearly 

 that the sex factors segregate at meiosis. TJie haploid spores grow into 

 gametophyte plants which are haploid and are either male or female, 

 and remain so under all experimental conditions. The factors deter- 

 mining this maleness or femaleness are genetic but have no effect in 

 the zygophase or sporophyte, which produces spores but shows no 

 differentiation into sexes or even any characters which could lead one 

 to call it bisexual. It is in fact asexual. But nevertheless it contains the 

 male and female factors, which can be wakened into activity if the 

 sporophyte is converted experimentally into a gametophyte. This con- 

 verson of phase takes place on regeneration; a small part of the diploid 

 sporophyte regenerates as a gametophyte, which is still diploid and 

 therefore still contains both the sex factors. It is found to be bisexual 

 and bears both male and female organs; since the male organs are 

 formed first during development, it can be spoken of as a protandric 

 hermaphrodite. It is sometimes also called an intersex, though this is 

 perhaps not strictly accurate since the plant is not intermediate, but is 

 both fully male and fully female at the same time. 



More complex hermaphrodites could be made by first obtaining 

 diploid gametopbytes with narcotics by suppressing a cell division 

 during spore formation. Representing the male factor by M and the 

 female by F, these gametopbytes obtained by producing double spores 

 were MM and FF, and were apparently normally male or female. By 

 crossing them tetraploid MMFF sporophytes were obtained and from 

 ^ Marchal and Marchal 191 1. 



