30 Brown: Apogamy in Phegopteris polypodioides 



under light conditions which not only proved sufficient for 

 the production of normal sporophytes but which failed to 

 retard their development in those cultures of the full solutions 

 which were renewed frequently. (2) In cases where apogamous 

 prothallia from a nutrient solution with one of the essential 

 elements omitted were transferred to a fresh full nutrient 

 solution, thereby permitting the vitality of the prothallia to 

 be renewed, no more apogamous outgrowths or sporophytes 

 were formed, although the cultures were kept under the same 

 light and temperature conditions. In some cases normal sporo- 

 phytes developed. The formation of these normal sporophytes 

 ceased as soon as the new solution was exhausted and the vitality 

 of the prothallia thereby lowered. (3) Some of the prothallia 

 which had developed upon a full nutrient solution, when removed 

 to a solution from which some essential element was omitted, 

 produced apogamous outgrowths or sporophytes as soon as 

 their vitality was reduced. However, relatively few were formed 

 under, these conditions because the prothallia of Phegopteris 

 polypodioides, when grown from the spores upon a full nutrient 

 solution which afforded the necessary elements for growth 

 and development, were unable to adjust themselves readily 

 to the physiological action of an incomplete solution. The 

 vitality of the prothallia seemed to be lowered so quickly that 

 it was impossible for them to make an attempt to overcome the 

 unfavorable condition for reproduction by producing apogamous 

 outgrowths and sporophytes. The prothallia of various species 

 of ferns seem to differ in this respect, some being more sensitive, 

 while others are more tolerant. (4) Apogamous prothallia 

 occurred frequently in uncrowded regions of the cultures where 

 light conditions were very good, while on the other hand in the 

 cultures of the full solutions normal sporophytes developed in 

 the most crowded regions where the light condition was the 

 poorest. 



The factor of temperature can not be considered as the 

 controlling factor in apogamy in Phegopteris polypodioides. 

 The prothallia in all cultures, both those which produced 

 normal sporophytes when the food supply was sufficient and 

 those which produced apogamous ones when the food supply 

 was insufficient., were kept under the same temperature condi- 

 tions. 



