128 Steil. — Apogamy in Nep hr odium hirtipes , Hk. 
in the sporangium of N ephr odium hirtipes may have preceded the appear- 
ance of apogamy. If the number of chromosomes was not at first reduced, 
the act of fertilization was rendered unnecessary, and hence the embryo may 
have arisen at first parthenogenetically and later apogamously. If the 
latter view is held, the double number of chromosomes would be present 
throughout the life-history. However, on the basis of other investigations 
of different apogamous species, it is probable that the chromosome number 
now characteristic of both generations of Nephrodium hirtipes is the original 
haploid number, and hence it seems likely that apogamy may have arisen 
before the incomplete nuclear divisions were established. These views 
regarding the origin of apogamy are similar to those expressed by Miss 
Allen ( 1911 ) with reference to Aspidium falcatum . 
Although so far no cytological evidence has been presented to confirm 
the occurrence of hybridization in ferns, it is possible that N ephr odium 
hirtipes and perhaps some other apogamous ferns may be of hybrid origin, 
and that the abnormalities which I have described have resulted from 
fertilization between two more or less closely related species. 
Summary. 
1. The prothallium of Nephrodium hirtipes is produced by the 
germination of a spore. 
2. The gametophyte never produces archegonia, but antheridia are 
formed which develop apparently normal antherozoids. 
3. The development of secondary prothallia is readily induced by 
cultural conditions. 
4. Attempts to induce an aposporous gametophyte development in 
this species have been successful only in rare instances. 
5. The embryo originates at an early stage in the development of 
the gametophyte as a vegetative outgrowth of the prothallium. The apical 
cell of the leaf is first formed, and then that of the root, and later that of the 
stem. A foot is never produced. The later stages in the development of 
the embryo resemble those of the ordinary fern embryo produced as 
a result of fertilization. 
6. At no time have nuclear migrations and fusions been observed 
to occur in the prothallium when the embryo begins its development. 
7. At the stage when the sporangium contains eight sporogenous 
cells, an incomplete nuclear and cell division occurs in each of these 
eight cells. As a result of the incomplete divisions, each nucleus con- 
tains the diploid number of chromosomes — between 120 and 130 . The 
eight sporogenous cells, now diploid, function as spore mother-cells. The 
spores formed from these cells have the haploid number of chromosomes — 
between 60 and 65 — and this number is retained in the cells of both the 
gametophyte and of the apogamously developed sporophyte. 
