22 Brown: APOGAMY IN PHEGOPTERIS POLYPODIOIDES 
cells elongated transversely instead of longitudinally and divided 
crosswise, giving rise to two distinct branches which in turn 
branched. Some of these branches, after broadening into fila- 
ments of two cells in width, reverted to a one-cell stage. Again 
a short filament was formed, which broadened out, and then, 
from this broadened region side branches were formed; the cells 
of the apical margin of the broadened portion also gave rise to 
branches which in turn formed other branches. Some of these 
branches, after forming either a long filament or a short one of 
only three cells, broadened into a prothallium bearing antheridia, 
after which it reverted to a filamentous condition. This capa- 
city of the prothallia to branch extensively seems to be of ad- 
vantage to the plant in enabling it to meet unfavorable en- 
vironmental conditions, by increasing the number of prothallia, 
thus giving rise to an extended area of rhizoids, as well as 
insuring the formation of a larger number of sporophytes, either 
normally or apogamously. Atkinson designates the branched 
prothallia of Adiantum cuneatum described by him as “starved 
prothallia,’’ and the author (’16) has shown that branching 
in various prothallia of the Polypodiaceae is intimately asso- 
ciated with conditions of nutrition, poor nutritive conditions 
accelerating the stimulus for branching and good nutritive 
conditions weakening it. Another interesting feature in connec- 
tion with the development of the young prothallia in the modified 
solutions was the frequency with which they met the unfavorable 
conditions for nourishment by reversion to a_ filamentous 
condition. Prothallia several cells in width and bearing antheri- 
dia would revert to a filamentous condition; then, after forming 
a filament three to eleven cells in length, they would broaden 
again to form a prothallium which in turn bore antheridia. 
Goebel considers a reversion to a juvenile form to be the result 
of unfavorable conditions, which in this case was doubtless an 
insufficient food supply. 
In the cultures which were kept in the laboratory, sexual 
organs, both male and female, developed on the prothallia in 
all the solutions, both modified and unmodified. They also 
developed on the few prothalia which survived on the unmodified 
solutions in the greenhouse cultures. Antheridia appeared in 
four to six weeks after the spores were sown. Both monoecious 
and dioecious prothallia occurred in the laboratory cultures on 
