270 Shaw . — The Fertilization of Onoclea . 
Embryos of Onoclea sensibilis from Series G. 
Fertilized 8 days, 1 embryo of 2 cells. 
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1 
This showed clearly that we should not expect to find 
the first division of the egg in these prothallia less than 
a week after fertilization, and, conversely, that the absence 
of embryos in the shorter series which had been prepared 
does not by itself indicate that they were abnormal. It was 
unfortunate that the specimens kept on the surface of the 
water did not cover a period longer than seven days. This 
failure was repaired as far as possible by fixing such a series 
from the cultures of the second species studied, but these 
plants were killed too late to be available for present 
purposes. It is also regretted that the long series of O. 
sensibilis was obtained after the prothallia had grown to 
a large size, and bore such large numbers of archegonia 
as to make the study of fertilization in these plants a more 
complex problem ; for at some certain time after reaching 
maturity the egg, if unfertilized, becomes atrophied to such 
an extent as to render normal fertilization impossible. Yet 
spermatozoids enter such eggs, and it has been suggested 
that their presence may then have some retarding influence 
on the development of the normally fertilized eggs on the 
same prothallium. On account of the long period occupied 
by the stages which it was proposed to follow, these Ferns 
are less suitable for the research than was expected. 
Methods. 
The cultures of Onoclea sensibilis were obtained by sowing 
spores on sterilized soil in earthenware saucers. Cultures 
