32 Brown: Apogamy in Phegopteris polypodioides 



regarded, as Bower ('88) has considered it, as a simplification 

 of the life cycle of the fern, or, in other words, as a response to 

 the changed environmental conditions for which a modified 

 life cycle is an advantage to the plant. Doubtless the prothallia 

 of all species of ferns possess this latent quality by virtue of 

 which they can respond to changed environmental conditions 

 by a reversion to this simplified life cycle, which was probably 

 the more primitive. 



For this and other reasons the value of the physiological 

 study of the gametophytes of ferns can hardly be overestimated 

 from the standpoint of determining the cause or causes of apoga- 

 my and as shedding light upon the physiological problems con- 

 nected with the interpretation of sexual phenomena and the 

 expression of the individuality of plants in their relation to their 

 environment. The latter point should be emphasized especially, 

 for it is not of so much importance that we determine the exact 

 factor of the environment, which works separately or together 

 with other factors in causing apogamy, as that stress be laid on 

 the individual physiological characteristics of the gametophyte 

 and sporophyte which cause them to respond to the stimulus 

 of the particular situation in the way best adapted to meet their 

 requirements. On account of these individual physiological 

 characterisctics of the gametophyte the same factor or group 

 of factors need not be the cause of apogamy in all species of 

 ferns. 



The fact that apogamy occurred frequently in Phegopteris 

 polypodioides under cultural conditions unfavorable for nourish- 

 ment would seem to indicate that apogamy is not a rare occur- 

 rence in this species and that it is easily induced. 



Summary 



i. The filamentous stage of the prothallia of Phegopteris 

 polypodioides, grown upon unmodified and modified Prantl's 

 and Knop's solutions, showed a great range of variability in 

 length, the greatest length occurring in the modified solutions. 



2. Branching of the prothallia and reversion to a filamentous 

 condition occurred frequently under unfavorable cultural 

 conditions. 



3. Sexual organs, both male and female, developed on the 

 prothallia in cultures of the unmodified solutions which were 



