No. 495] SYMBIOSIS IN FERN PROTHALLIA 163 



Of the ferns with green prothallia, the endophyte has 

 been found, almost without exception, in the following: 

 Marattia Douglasii Baker, Kaulfussia cesculifoh'a Bl., 

 Angiopteris evecta Hoffm., Oleiclienia (Eugleichoria) 

 polypodioides Sm., G. (Mertensia) dichotoma Willd. 

 (=G. linearis (Burm.) Bedd), G. {Mertensia) laevigata 

 Hooker, G. (Mertensia) pectimta Presl. In Osmunda 

 cinnamomea it appears to be commonly but not always 

 present, and in 0. Claytoniana it could not be found. 

 The number of slides of the last species examined was 

 not very large and it is possible that further study of 

 this species, as well as of 0. regalis, will show its further 

 occurrence in the Osmundacere. 



Of the forms that were examined, that occurring in 

 Osmunda and Gleichenia was the largest (Fig. 3, B, C) 

 and equal in size to the endophyte of Ophioglossum. The 

 form in Angiopteris was the smallest that was seen. 



The Significance of tiie Endophyte 

 That the presence of the endophyte is necessary to the 

 existence of all strictly saprophytic gametophytes is in- 

 dicated by the failure of the germinating spores to 

 develop unless they become associated with the fungus. 

 Moreover, the universal occurrence of a similar endo- 

 phyte in all humus-saprophytes among the seed plants 

 indicates that in all of these chlorophylless plants the 

 presence of the fungus is necessary for the existence of 

 the host. Although it has not been directly proved, it 

 is generally assumed that one role of the endophyte is 

 the elaboration of some of the carbonaceous constituents 

 of the humus. The infrequent communication between 

 the external hyphae and the internal mycelium makes it 

 unlikely that the nutritive products are directly absorbed 

 by the fungus, and it seems much more probable that the 

 rhizoids of the gametophyte are the direct agents of 

 absorption. How the humus constituents are changed 

 by the action of the fungus so that they are available for 



