LIBRARY 

 NEW YO*K 

 BOTANICAL 



Q AH DEN 



Reprinted from the Bulletin of the Torrey Botanical Club, Vol. 50, No. 1 , 



January, 1923. 



Apogamy in Phegopteris polypodioides* 



Elizabeth Dorothy Wuist Brown 



(with twenty text figures) 



Introduction 



The wide-spread occurrence of apogamy in various genera 

 of ferns has led to a great deal of investigation of the subject. 

 In most of this study, however, greater emphasis has been laid 

 upon the morphological and cytological than upon the physio- 

 logical phase. 



Leitgeb ('85), who was the first to study apogamy from this 

 latter point of view, carried out a series of experiments to deter- 

 mine the light reactions of apogamous fern prothallia. Among 

 the things he discovered was the fact that when prothallia of 

 Aspidium falcatum bearing very young sporophytes were illumi- 

 nated from the ventral side, the sporophytes were suppressed, 

 new ones being formed on the dorsal side. In rare cases both 

 dorsal and ventral sporophytes would survive and then they 

 seemingly would give rise to a single sporophyte, with its 

 various parts on both sides of the prothallium. Leitgeb con- 

 siders the alterations of the light relations, during the growth 

 of the prothallia, to be the probable cause of some of the modi- 

 fications in the apogamous sporophytes described by DeBary 



('78). 



Bower ('88), although he did not make a physiological 



study of apogamy. calls attention to the importance of the 



environmental conditions in the life history of a fern. He cites 



the fact that the Hymenophyllaceae are exceedingly susceptible 



to changes of moisture in the air, and concludes that such 



changes react upon their mode of growth. 



Lang ('98) found, in the case of nine different ferns, that by 

 exposing the prothallia to direct sunlight and watering them 

 from below, a condition favorable for vegetative growth but 

 preventing fertilization, sporophytes were produced, although 

 ^ome of them were aborted. 



Nathansohn ('00), experimenting with Marsilia Drummondii, 

 concluded that exposure to higher temperature for a limited 



* Contribution from the Osborn Botanical Laboratory. 



17 



