Brown: Apogamy in Phegopteris polypodioides 29 



The pro thallium, upon which the apogamous outgrowth 

 formed as a 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 Fig. 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 Fig. 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 Fig. 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- 



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 



