20 Brown: Apogamy in Phegopteris polypodioides 



nutrient solutions. About six months later, cases of apogamy 

 were observed in cultures on Prantl's solution from which the 

 NH4NO3 had been omitted. In view of the small number of 

 such cases, however, it was thought best to repeat the experi- 

 ments, and also to make cultures from spores of the same species 

 whose sporophytes had grown under normal environmental 

 conditions. In this way it was hoped that it might be possible, 

 by a comparison of the results obtained, to determine whether 

 apogamy was characteristic of this species, and, if so, under what 

 environmental conditions this condition was induced. 



For this purpose, during the following summer (1916), fresh 

 spores were obtained from the same plant at Ithaca and also 

 from wild plants at Brooklin, Maine (the latter through the 

 courtesy of Dr. A. H. Graves). Cultures of these were started 

 early in October on Prantl's and Knop's full nutrient solutions; 

 on modifications of Prantl's solution from which NH 4 N0 3 , 

 K 2 S0 4 , NaCl, CaS0 4 , MgS0 4 , Na 3 P0 4 , and both NaCl and 

 Na3P0 4 , respectively, were omitted; and on Knop's solution 

 minus the Ca(NO„) 2 . In preparing the cultures, about 25 cc. of 

 the nutrient medium was poured into a small glass dish, a drop 

 of a 1 per cent solution of ferric chloride added, and the spores 

 sown upon the surface of the solution. The dishes were covered 

 with loose-fitting glass tops. Two series of cultures were pre- 

 pared from each of the two lots of spores, one of which was placed 

 in the greenhouse in bright light, the other in the laboratory 

 before an east window. The germinating prothallia, instead of 

 being transferred at intervals to fresh solutions (as had been 

 done the preceding year) were allowed to remain upon the original 

 solution on which the spores were sown, and the increasingly 

 unfavorable conditions of environment which thus resulted 

 were further enhanced by a luxuriant growth of algae which 

 developed in all the dishes. 



Development of the prothallia 



Practically no difference was noted in the germination of 

 the spores or in the early development of the prothallia from the 

 two sources. Germination began in about one week after the 

 spores were sown. The early growth and development of the 

 prothallia was rapid in all the cultures, but later it varied accord- 

 ing to the particular solution upon which they were growing. 



