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 
some of them were aborted. 
Nathansohn (’00), experimenting with Marsilia Drummondit, 
concluded that exposure to higher temperature for a limited 
* Contribution from the Osborn Botanical Laboratory. 
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