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 



