Steil. — Apogamy in Nephrodium hirtipes , Hk. \ 2 7 
of two vegetative cells of the prothallium, the haploid number of chromo- 
somes characterizes the gametophyte, the diploid number the sporophyte. 
In Aspidium falcatum , in which according to Miss Allen (1911) the fusion 
is between sporogenous cells, chromosome reduction immediately following, 
the haploid number of chromosomes is characteristic of both generations. 
So far as the chromosome number is concerned the same condition prevails 
in Nephrodium hirtipes as in Aspidium falcatum. 
The chromosome number in other apogamous ferns, so far investigated, 
is of interest. As a result of induced apogamy in Nephrodium molle , 
according to Yamanouchi (1908 a, b, and c) the haploid number is found in 
both the gametophyte and the sporophyte. Farmer and Digby (1907) 
think that in Lastraea pseudo-mas var. cristata apospora both generations 
possess the haploid number of chromosomes. On the other hand, the same 
investigators found that in Athyrium Filix-foemina var. clarissima, Jones, the 
diploid number of chromosomes persists throughout both generations. Thus 
it appears from the studies so far made of apogamous ferns, as well as by 
evidence from other groups of plants, that the characteristic differences 
between gametophyte and sporophyte are not determined alone by differ- 
ences in the chromosome number, but that the sharply contrasted develop- 
mental possibilities of spore and zygote are governed by other factors 
which are as yet entirely unknown. 
Apogamy in ferns developed in all probability at a late period in the 
evolution of the homosporous ferns. So far no certain case of apogamy has 
been discovered in the Eusporangiatae. Jeffrey (1896), however, believed 
that he found in one instance evidence of apogamy in Botrychium virgini- 
anum. A large number have been found among the Polypodiaceae, the 
most highly specialized, and probably the most recent, homosporous lepto- 
sporangiate family. 
In regard to the origin of apogamy in Nephrodium hirtipes three 
possibilities are presented. If at one time in the life-history of the fern 
fertilization was by some means suppressed, the archegonia may have 
disappeared and fertilization have thus been rendered impossible. The 
embryo may then have arisen as a vegetative outgrowth. As a substitution 
for fertilization the incomplete divisions described in this paper may have 
occurred. Why a doubling of the number of chromosomes should still 
be necessary for the maintenance of the life-cycle is difficult to explain, 
since, as has just been stated, in Lastraea pseudo-mas var. cristata apospora 
the haploid number of chromosomes remains unchanged throughout both 
generations, and although Yamanouchi (1908) did not investigate sporo- 
genesis in the apogamously produced sporophytes of Nephrodium molle , it is 
probable that the gametophyte number is maintained in both generations of 
the fern. 
On the other hand, the occurrence of incomplete nuclear divisions 
