too Etter: PoLYEMBRYONY IN POLYPODIACEOUS FERNS 
possible to determine the presence or absence of embryos and 
their number, but after some experience it was not at all difficult 
to be reasonably sure, so that only those prothallia with two or 
more embryos were fixed, and after fifteen days it was rarely 
necessary to section, although it was always done when there 
was any room for doubt. 
The vigorous gametophytes, 3-5 mm. across the lobes at 
the time of fecundation, gave better results than the older ones, 
although polyembryony was found among prothallia 6-8 mm. 
across the lobes. This may be accounted for by the fact that 
the young prothallia adjusted themselves more readily to the 
new environment when transplanted than did the older ones, 
although in each case the same care was used in handling. 
In some instances two embryos developed almost equally, 
and beyond a doubt would have become independent sporo- 
phytes; this is well illustrated by PLATE 4, FIGS. I-3. FIG 
is a diagram of a longitudinal section of a prothallium seven 
days after fecundation, illustrating the location of two embryos 
of almost equal size about 0.5 mm. apart on the archegonial 
cushion. Each embryo has approximately seventy-five to one 
hundred cells, and the meristematic condition of the venters is 
indicative of all that should be expected in healthful embryos. 
Fic. 3 (0, of Fic. 1) was slightly to one side and a little back of 
Fic. 2 (a, of Fic. 1). The embryo of Fic. 2 sue have a few 
more cells, but it is located slightly nearer the si 
FIG. 4 is a diagram of a longitudinal section PH a idialieatt 
ten days after fecundation, showing the location of two em- 
bryos of very unequal size (a and b). It is clearly evident that 
the smaller embryo (6) is being starved or at least that some 
factor is working to its disadvantage. The larger embryo (a 
and FIG. 5), on the contrary, is normal in all respects. If these 
embryos had been on a more vigorous gametophyte, there is 
little doubt that they would have become independent in their 
existence, but such is not to be expected from the common run 
of prothallia, especially when one embryo is considerably nearer 
the sinus. 
To determine what would result from a fecundated egg in a 
prothallium which had an embryo already started at the time 
of selective fecundation, several very vigorous prothallia were 
selected each of which bore an embryo about twenty-five days 
