434 Mr Gregory, Some observations upon 



occurrence of a male prothallium can only be ascribed to chance 

 conditions of nutriment and age (see also Heim ('96)). There 

 can be no doubt that in this Fern all the prothallia possess the 

 power to form female organs 1 ; but, since the production of a 

 sporophyte must be some tax upon the gametophyte, only those of 

 vigorous and full growth bear the female organs. With this we 

 may compare the results which Klebs obtained in experiments 

 upon the conditions of reproduction. Although able to delay the 

 production of the female organs, he was not able, by artificial 

 means, completely to eliminate them. 



(2) The Sex of the Gametophyte. 



From the experiments upon Ferns recorded above may be 

 drawn two conclusions : 



(1) that, although spore-formation is preceded by a quali- 

 tative reduction division, no segregation of the sex- characters has 

 taken place at that division ; 



(2) that the form of gamete (antherozoid or ovum) pro- 

 duced by any prothallium is subject within limits to influence 

 through the conditions of nutrition ; that is, that all the prothallia 

 have the power of producing either form of gamete, although 

 under some conditions the production of one form may remain 

 in abeyance. 



I would suggest that these conclusions are equally true of all 

 those higher plants in which the individual sporophyte bears both 

 megasporangia and microsporangia ; and that the second con- 

 clusion is true also of those plants in which the sporophyte is 

 dioecious. 



The heterosporous hermaphrodite sporophyte is to be looked 

 upon as derived directly from the isosporous form, remaining like 

 the latter undifferentiated as regards the separation of the sexes ; 

 as a consequence no segregation of the sex-characters which 

 appear in the sporophyte takes place ; and all the gametes which 

 are produced carry the hermaphrodite character, which reappears 

 in the next sporophyte generation. The production of one form 

 of gamete to the exclusion of the other, by the gametophyte of 

 such plants, is then a phenomenon distinct from the separation of 

 the sexes in the sporophyte generation. 



The spores derived from one spore-mother-cell, in heterosporous 



1 The prothallia of Onoclea are said to be strictly dioecious (Campbell ('95) ; p. 310) . 

 A cytological examination of spore-formation in that Fern was therefore made to 

 see whether any features might present themselves which might indicate a cyto- 

 logical basis for the separation of the sexes. Only a negative result was forthcoming, 

 the divisions leading to spore-formation having an exact similarity with those of the 

 other Leptosporangiate Ferns examined. 



