Brown: APOGAMY IN PHEGOPTERIS POLYPODIOIDES 29 
The prothallium, upon which the apogamous outgrowth 
formed asa lobe in the sinus, was irregularly heart-shaped and 
bore archegonia on a well-developed meristem (FIG. 19). 
With the exception on the one shown in Fic. 16, all the pro- 
thallia upon which apogamous outgrowths originated as cellular 
masses on the archegonial cushion were distinctly notched, and 
the apogamous outgrowths first appeared as conical cellular 
masses, the apices of some being more pointed than others. 
However, the outgrowth shown in Fic. 18 varied somewhat 
in its development. Beginning as a cellular mass, it formed 
an elongated, slightly flattened and thickened prothallus-like 
structure, which in turn reverted to a filamentous condition. 
The apogamous sporophyte shown by Fic. 17 began its 
development as a cellular mass near the sinus on the archegonial 
. cushion of an irregularly shaped prothallium. From this mass 
there developed first two structures intermediate between 
leaves and prothallia and then a root. The first of these inter- 
mediate structures resembled a very much elongated prothallium 
one cell in thickness with an expanded and irregularly lobed 
apex. The second was curled at first in the same way as a 
normal leaf but resembled the first in being an elongated prothal- 
lus like structure one cell in thickness. The root appeared nor- 
mal. 
DISCUSSION 
The factors which are considered as the possible controlling 
or influencing ones in apogamy, as advanced by the previously 
mentioned workers, are the following: (1) insufficient water 
for fertilization, (2) weak light, (3) bright light, (4) high tem- 
perature, (5) poor soil. In the opinion of five of the writers 
cited, lack of sufficient water to permit fertilization to take 
place is regarded as the controlling factor in the particular 
ferns with which they worked. In the case of Phegopteris 
polypodioides, as well as in the other cases of apogamy previously 
described by the author (’19, ’20), this factor can be entirely 
eliminated, since the prothallia were grown upon a liquid 
medium. 
Also the factor of light, either bright or weak, can not 
be considered as the most important one in these cases of 
apogamy for the following reasons. (1) All cultures were kept 
