3o8 MOSSES AND FERNS chap. 



with the former family. It, however, also resembles that of the 

 Cyatheacese as well, and the strongly -developed indusium is 

 much like that of the latter. The Schizaeaceae also may 

 possibly form a side branch from the ascending series which 

 ends in the Polypodiaceae. 



As these latter are the typical modern Ferns, it will be best 

 to trace the development of the plant here before considering 

 the variation found in the other families. The spores of the 

 genus Onoclea are especially suited to studying the germination 

 and development of the prothallium, and we will follow this 

 in O. struthiopteris i^Strnthiopteris Germanicd), the well-known 

 Ostrich Fern. 



The large oval spores contain, besides much oil and some 

 starch, numerous small crowded chloroplasts. The three walls 

 of the spore are plainly demonstrable, especially as the brown 

 perinium is often thrown off by the swelling of the spore, and 

 the transparent exospore can then be seen, with the delicate 

 endospore lying close to its inner face. A large nucleus 

 occupies the centre of the spore. Contrary to the statements 

 usually made that spores containing chlorophyll quickly lose 

 their vitality, these will germinate after a year or more, although 

 not so well as those of the same season, but they normally 

 remain from autumn until spring before they germinate. O. 

 sensibilis acts in the same way, and spores of other Ferns 

 containing chlorophyll have been germinated after an equally 

 long period. 



The spores germinate promptly, varying from two or three 

 days to about a week, depending upon the temperature. The 

 exospore is ruptured irregularly near one end, and through this a 

 short colourless papilla protrudes and is shut off by a transverse 

 wall (Fig. 156, B). This papilla contains little or no chloro- 

 phyll and rapidly lengthens to form the first root-hair, which 

 undergoes no further divisions. The large green cell alone 

 produces the prothallium. The divisions in the prothallial 

 cell vary somewhat, but in the great majority of cases a series 

 of transverse walls is first formed, and the young prothallium 

 (Fig. 156, C) has the form of a short filament. Sooner or 

 later, in normally-developed prothallia, the terminal cell of the 

 row becomes divided^ by a longitudinal wall, which may be 

 straight, but more frequently is oblique and followed by another 

 similar wall in the larger of the two cells, meeting it so as to 



