GLEICHENIACEAE 



[CH. 



today, while less certain indications of both types reach back to the 

 Palaeozoic Period. 



The Gametophyte 

 The prothalH of Stroviaioptevis and of Platyzoma are unknown: observa- 

 tions are therefore restricted to the sections Dicranopteris and Eu-Gleichenia, 

 but it will be seen that they present features of phyletic significance. The 

 prothallus was first described by Rauwenhoff {Arch-Ne'er, xxiv, 1891, p. 157), 

 but his observations have been extended into further detail by Campbell 

 {Bull. Jard. Bot. Biiit. viii, 1908, p. 88). It corresponds in development to 

 that of the Polypodiaceae, though it may have a midrib like that of Osmunda, 

 and has like it abundant adventitious growths formed upon the margin or 



Fig. 494. Antheridia of the genus Gleichenia, showing their variability, 

 and the large size of some of them: i, ii, G. laevigata (102, 35 

 spermatocytes in sections): iii, G. pectinata (66): iv, v, G. dicho- 

 toiiia (33, 45): vi, G. polypodioides (19). (All after Campbell.) 



the ventral surface, and developing into normal prothalli (compare Camp- 

 bell, Mosses and Ferns, 3rd, Edn. Fig. 208). The habit is almost that of 

 Fossombronia: old prothalli contain an endophytic fungus. The archegonia 

 have a long and straight neck, as in the Osmundaceae, and are scattered 

 over the whole thickened midrib. The antheridia present more important 

 features: they have been examined in several species. They are mostly 

 large, and resemble those of Osninnda. In G. laevigata the diameter 

 may reach loo/i, and each may contain several hundred sperm-cells: in fact 

 those of G. laevigata d^wA pectinata are larger than those of any Leptospor- 

 angiate Fern yet described (Fig. 494, i, iii). But this size is not constant for 

 the species: when crowded, smaller antheridia may be formed (Fig. 494, ii), 

 and these may contain fewer spermatocytes. 



Reference has already been made to the parallel between spore-number 

 and spermatocyte-number in various Ferns (Vol. I, p. 291). In no genus of 



