716 U. Ndj 



THREE TYPES OF GAMETOPHYTES IN CULTURES OF 

 PTERIDIUM AQUILINUM 



Mature gametophyte cultures of PtericUum aquilinum, and of 

 many other homosporous, leptosporangiate fern species, contain two 

 types of prothalli. Some bear anthcridia only and are commonly 

 designated the male prothalli. They lack a meristem (hence their 

 diffuse growth habit and random shape) and are for this reason occa- 

 sionally also referred to as the ameristic prothalli. This latter desig- 

 nation is used in this report for reasons that will become apparent 

 below. Others bear only archegonia and are commonly called the 

 female prothalli. Such observations on mature cultures led to the con- 

 cept that the female prothalli failed to form antheridia under normal 

 conditions of culture or formed them only rarely, especially under 

 atypical conditions of culture (2,4,5,8,16). In contrast, Czaja (3) 

 came to the conclusion that the female gametophytes formed anther- 

 idia regularly at an early stage of development but discontinued 

 their formation as they attained the archegonial phase. 



It could be demonstrated that the archegonial phase is, in many 

 prothalli of Pteridium aquilinum, actually preceded by an antheridial 

 phase. At the same time it was shown that some individuals of the 

 gametophyte population, to wit, the most rapidly growing and devel- 

 oping ones, attained the archegonial phase without a prior antheridial 

 phase (10). 



The occurrence of the two types of archegonium-forming prothalli 

 led to the hypothesis that the prothalli of Pteridium aquilinum be- 

 come insensitive to the antheridial factor before they begin to pro- 

 duce it at effective concentrations. This hypothesis was considered 

 established when it was demonstrated that all individuals of the 

 gametophyte population failed to form antheridia if they were grown 

 one per flask, and that all prothalli formed antheridia if they all 

 were exposed to antheridial factor while they were still sensitive to 

 it (10). 



The antheridia a gametophyte forms thus arise in response to 

 antheridial factor that is secreted into the medium by more rapidly 

 developing individuals of the gametophyte population (which them- 

 selves have already become insensitive to it). Accordingly, the most 

 rapidly developing gametophytes in a culture of Pteridium aquili- 

 num attain the archegonial phase without a prior antheridial phase 

 because they are without a supply of antheridial factor while they 

 are still sensitive to it. 



A gametophyte population of Pteridium aquilinum thus contains 

 three types of individuals: Archegonium-forming prothalli with a 



