lel Se ee 
Branched cells in the prothallium of Onoclea sensibilis L, 
CAROLINE A, BLACK 
(WITH PLATES 22 AND 23) 
The fern gametophyte offers an interesting field for experi- 
mental culture work, not only in regard to the reproductive organs 
as various writers have shown, but in the germination of the spore 
and the development of the prothallium. Material is readily 
procured and the growing conditions may be easily controlled. 
The average fern spore will germinate on water or moist soil and 
the prothallium lives about three or four months or until a 
sporophyte has been established. Many have been known to live 
much longer. 
The normal development of the gametophyte of different 
ferns has been described by various writers. In a recent research 
on the prothallium of Camptosorus rhizophyllus (L.) Link, Pickett 
(1) found that the prothallia showed a wide variation in size and 
form. The apical group is usually unsymmetrically placed and 
the typical wedge shaped apical cell is rarely seen. Old prothallia 
were found with several marginal growing regions and _ prolifer- 
ations capable of independent growth were produced. In some 
very interesting experiments with this fern Pickett (2) had already 
shown that the drought resisting character of these prothallia was 
an efficient factor in the establishing of this fern to its habitat. 
The dioecious prothallia of Onoclea Struthiopteris (L.) Hoftm. 
have been the subject of a physiological problem by Miss Wuist, . 
(3) who has obtained monoecious forms in this fern by growing 
prothallia in culture solutions. Monoecious prothallia were also 
observed in soil cultures. Miss Wuist mentions the appearance 
of irregular and filamentous forms, some exceedingly long, in these 
cultures. Mottier (4) working with the same fern finds that 
about 12 per cent. of the prothallia are monoecious under optimum 
culture conditions. Branched filamentous prothallia have been 
described by Miss Pace (5) in fern gametophytes. Many examples 
617 
