342 Proceedings of the Ohio State Academy of Science 



gard to the reduction division. Many are not able to get be- 

 yond the erroneous idea that the reduction (hvision must in 

 some way be a maturation division when in most plants it has 

 nothing whatever to do with the development and ripening of 

 gametes. 



But to return to the question of sex determination ; in 

 Isoetes, according to Smith, each leaf bears but one sporan- 

 gium and the sporangia are apparently all alike in the early 

 stages. Up to the time when the archesporium is 8 to lo cells 

 deep in cross section there is no histological feature by which 

 one may determine whether a given sporangium will ])roduce 

 microspores or megaspores. The first changes to be seen that 

 mark the microsporangium are those which lead to the differ- 

 entiation of the sporocytes. The sex of the future gameto- 

 phytes is. therefore, determined in the early stages of the sporo- 

 cytes if not earlier. The nature of the sporophylls of Selagi- 

 nella kraussiana must be determined in the incipient stage, for 

 the one megasporophyll always has a definite position in rela- 

 tion to the numerous microsporophylls. 



As far back as i88i, Prantl found that if fern thalH are 

 cultivated with aboundant nutriment, only ovaries are developed, 

 while with poor nourishment spermaries are formed. The sex 

 of these potentially hermaphrodite juvenile individuals is thus 

 determined by their environment during vegetative growth. 

 Moreover, by keeping them in suitable conditions they may be 

 kept as male and female, the ordinary hermaphrodite tendencies 

 never coming to expression. 



Douin finds that in the unisexual liverwort, Sphaerocarpus 

 terrestris about 75 per cent, of the spore tetrads clearly show 

 two males and two females. There were, however, several 

 cases clearly anomalous. One group of two tetrads had five 

 males and three females. Another tetrad had three males and 

 one female, and two others had one male anrl three females. 

 Apparently the sex in this plant is determined at the time of the 

 reduction division. But I do not think that the 75 per cent, is 

 high enough to warrant a final conclusion. At least 90 per cent, 

 of the tetrads should be taken into account before one could 



