Physiology of Anthcridium Formation in Ferns 711 



antheridium formation in Anemia phyllitidis (11) but is inactive to- 

 ward the species used to assay for the Pteridium factor. In Lygodiiim 

 japojiicii7n antheridium formation seems to be controlled by still 

 another substance (12) even though this species belongs to the same 

 family as A. phyllitidis (Schizaeaceae). 



The application of the Anemia factor to young cultures of Anemia 

 phyllitidis led to the onset of the antheridial phase while the pro- 

 thalli were still at a juvenile (filamentous) phase (Figure ID, arrows 

 indicate antheridia). Control prothalli (Figure IE) were invariably 

 free of antheridia even at the much more advanced stage of develop- 

 ment pictured in Figure IF. 



It is apparent from these studies that antheridium formation is 

 controlled by different substances in different groups of ferns. It 

 should also be stressed that within the wide range of species respon- 

 sive to the Pteridium factor, the minimally effective concentrations 

 vary widely. Thus the prothalli of Dennstaedtia punctilobula failed 

 to respond unless they were supplied with the Pteridium factor at a 

 concentration about 125 times higher than was necessary in the 

 prothalli of Onoclea sensibilis and of Pteridium aquilinum itself. In 

 the prothalli of Woodsia obtusa the minimally effective concentra- 

 tion of the Pteridium factor exceeded that required for antheridium 

 formation in Onoclea sensibilis by a factor of about 25 (11). 



The possibility must therefore be considered that the factors con- 

 trolling antheridium formation in these species are actually different 

 but structurally so closely related that the factor produced by Pter- 

 idium aquilinum is capable of bringing about antheridium forma- 

 tion also in Dennstaedtia punctilobula and in Woodsia obtusa if it 

 is supplied at a high enough concentration. Raper (14) also considers 

 the possibility that hormonal specificities account for the failure to 

 obtain oospores in some of the attempted interspecies and interge- 

 neric crosses of water molds. 



The above results raise a question of biological specificity. The 

 studies of Kluyver and Van Niel have drawn attention to the simi- 

 larity, even identity, of basic biochemical patterns in taxonomically 

 widely separated organisms. It is tempting to postulate that the 

 metabolism associated with antheridium formation, i.e., an event 

 that we conceive of mainly in morphological terms, is also similar in 

 different fern species. The above results may be reconciled with such 

 a postulate if we consider that the induction of an antheridium is 

 likely to involve many reactions and compounds. Antheridium for- 

 mation in Pteridium aquilinum. Anemia phyllitidis, and Lygodium 

 japonicum might thus be controlled by different factors because dif- 

 ferent reactions became rate-limiting during evolution. Alternatively, 

 we might be witness to evolution on a molecular level. On this as- 



