Brown: Apogamy in Phegopteris polypodioides 31 



Poor soil as a factor in causing apogamy would be operative 

 either through the absence of the elements necessary for develop- 

 ment, or the presence of those elements in such a form as not to 

 be available for the use of the prothallia. In either case it 

 would be a lack of sufficient nourishment which would be the 

 stimulus to apogamy. The results secured on poor soil would 

 compare with those obtained in Phegopteris polypodioides where 

 the apogamous outgrowths and sporophytes were due to in- 

 sufficient nourishment. The proof for this is the fact that no 

 cases of apogamy were observed in cultures of the full nutrient 

 solution when it was renewed frequently; or, in other words, 

 when a sufficient food supply was available. Also, apogamous 

 outgrowths and sporophytes ceased to develop, and in some 

 cases normal sporophytes were formed, when the nutrient 

 solutions were renewed in the cultures, although other factors 

 remained the same. Still further evidence is the fact that 

 frequently the apogamous outgrowths showed a reversion from 

 a more or less complex structure, several cells in thickness, 

 bearing tracheids to a simple prothallus-like body only one cell 

 in thickness and branched, indicating a still greater lowering 

 of the vitality, which was doubtless due to an insufficient food 

 supply. 



Prantl's ('81) work on the nutrition of ferns, Klebs's ('93) 

 valuable studies on the physiology of reproduction, and the 

 work of others have demonstrated that an intimate connection 

 exists between nutrition and growth, and between growth and 

 reproduction. Since both growth and reproduction are depend- 

 ent upon nutrition, it would seem as if nutrition was the 

 most important if not the controlling factor in causing apogamy. 

 Farmer and Digby ('07), Winkler ('08), Allen ('11), and others 

 are of the opinion that the morphological characters of the game- 

 tophyte and sporophyte are not determined by the chromosome 

 numbers as such. It would seem as if the morphological features 

 were determined to a large extent by physiological characteristics, 

 and that the difference between the gametophytic and sporo- 

 phytic tissue was not a marked one physiologically. Apogamy 

 seems to be due in all cases to a lowering of the vitality of the 

 prothallia to such an extent that normal sporophytes can not 

 be formed. This may be brought about by one or more factors 

 working separately or together. Therefore, apogamy may be 



