TO THE KNOWLEDGE OF PLATYZOMA MICROPHYLLUM. 
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marked sexual distinctions are seen only in the established gametophytes. There 
is no a priori reason why differences in the size of sporangia and spores should 
not accompany true homospory, for the nutrition of the individual sporangium 
might conceivably lead to these differences, without involving sexual distinctions 
in the gametophytes. The balance of evidence is, however, clearly in favour of 
heterospory when marked differences in the size of sporangia and spores occur ; 
but the homosporous or heterosporous condition of any fern is demonstrable only 
after germination. In certain instances, as in Ceratopteris, which are considered 
Text-fig. 2. 
Text-fig. 3. 
Text-fig. 4. 
Text-fig. 5. 
homosporous, poorly nourished prothalli are small, and bear only antheridia. The 
more robust prothalli are bisexual or female. It may be that, as with the gameto- 
phytes of Ceratopteris , so also with the sporangia and spores of Platyzoma, the sex 
of the individual is a concomitant of its nutrition. 
The materials of Platyzoma available were unsuitable for the study of sporangial 
development. The number and fate of the spore-mother cells in the two sporangial 
types is, then, unknown. The spores have not been germinated, and the nature of the 
gametophytes remains uncertain. In the absence of information on these important 
points the facts now to be detailed regarding the mature sporangia and spores may 
indicate the importance of the mixed sporangial characters, and will link, at a later 
date, the facts of sporangial development with those of gametophyte construction. 
