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 
erns. 
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 
1. 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 
