189 
Apogamy in Ferns. 
plants in which spores (and the meiotic phase) are cut out of the life-cycle, 
and the gametophytes arise directly as outgrowths from some part of 
this sporophyte — whether from barren sporangia or from the tissues of 
the leaves, and retain the full sporophytic (premeiotic) complement of 
chromosomes. The varieties clarissima of the Lady Fern may be cited 
as examples amongst the Ferns. Perhaps a third group should be added 
in which there is reason to think (e. g. Lastrea pseudo-mas var. cristata 
apospord) that the sporophyte only retains the original gametophytic 
chromosomes, but as in this form apospory and apogamy regularly 
follow each other, and the gametophyte now resembles the sporophyte 
in its chromosome contents, it is better to avoid increasing the com- 
plexity of classificatory systems by inventing a special class for such 
cases. 
Most people would probably agree with us in regarding the type 
of apogamy, as illustrated by the polydactyla varieties, as simpler 
and less modified than that which involves apospory as well. The 
prothallia of many Ferns belonging to the former series are apparently 
normal, and they are certainly so during their earlier life. Thus we meet 
with facultative apogamy in the latter, which passes into obligate apogamy 
in those Ferns which have lost the power of producing archegonia. In the 
cases examined, the method of doubling the chromosomes of the gameto- 
phyte by ordinary fertilization is replaced by the fusion of nuclei belonging 
to prothallial cells. There is very strong evidence to show that this latter 
process obtains in prothallia that have arisen from fertile spores, but which 
by cultural conditions have been prevented from forming sporophytes other 
than in an apogamous manner, for Lang 1 observed and figured binucleated 
cells in his prothallia of Scolopendrium vulgare, very similar to those we 
have found in Lastrea. On the other hand, when the prothallium arises 
aposporously, as in the varieties of A thy Hum, in Lastrea pseudo-mas var. 
cristata apospora, and in Scolopendrium vulgare var. crispum Drummondae, 
no such nuclear fusion has been detected. The cases are closely paralleled 
by what is known to occur when meiosis is omitted elsewhere. Thus 
Overton 2 found that in Thalictrum purpurascens the embryo could arise 
with or without fertilization. He adduced convincing evidence to prove 
that in the latter case meiosis had been suppressed, and that the oosphere 
itself possessed the full premeiotic complement of chromosomes. Such 
a case, which is not one of parthenogenesis, but a true case of apogamy, 
is very similar to that of A thy Hum Filix- foemina var. clarissima, Bolton, 
and the Drummondae variety of the Hart’s-tongue. The chief difference 
is that in the Athyrium the gametophyte springs from premeiotic sporangial 
1 Lang, loc. cit. 
2 Overton, J. B., Ueber Parthenogenesis bei Thalictrum purpurascens . Ber. d. Deutschen 
Bot. Gesellsch. , Bd. xxii. 
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