IX MARATTIACE.^-ISOETACEJE 259 



plant. The duration of the prothallium is apparently unlimited, 

 so long as it remains unfecundated. The writer kept prothallia 

 of Marattia Doiiglasii for nearly two years, during which they 

 grew continuously and finally reached a length of over two 

 centimetres. At the end of this time they were growing 

 vigorously, and there was nothing to indicate the slightest 

 decrease in their vitality. 



The prothallia are monoecious, although not infrequently 

 the smaller ones bear only antheridia. The latter always 

 appear first, and are mainly found upon the lower side of the 

 midrib, but may also occur upon the upper side. The arche- 

 gonia are confined to the lower surface of the midrib, and as 

 they turn dark brown if they are not fertilised, they are visible 

 to the naked eye as dark brown specks studding the broad 

 thick midrib. Both antheridia and archegonia resemble closely 

 those of the Ophioglossacea;. 



The antheridium arises from a single superficial cell which first 

 divides into an inner cell, from which the sperm cells are derived, 

 and an outer cover cell (Fig. 133, A). The latter divides by 

 several curved vertical walls (Figs. E-G) which intersect, and 

 the last wall cuts off a small triangular cell (c), which is thrown 

 off when the antheridium opens, and leaves an opening through 

 which the sperm cells are ejected. The inner cell, by repeated 

 bipartitions, gives rise to a large number of polyhedral sperm 

 cells. Before the full number of these is complete, cells are cut 

 off from the adjacent prothallial cells, which completely enclose 

 the mass of sperm cells. As in other Archegoniates, the 

 nucleus of the sperm cell, after its final division, shows no 

 nucleolus. The first sign of the formation of the spermatozoid 

 that could be detected was an indentation upon one side, 

 followed by a rapid flattening and growth of the whole nucleus. 

 The cytoplasmic prominence which, according to Strasburger,^ 

 is the first indication of the formation of the spermatozoid, 

 could not be certainly detected. The main part of the sperma- 

 tozoid stains strongly with alum-cochineal, and is sharply differen- 

 tiated against the colourless cytoplasm, and for some time shows 

 the characteristic nuclear structure. The origin of the cilia was 

 not very clearly made out, but probably, as Strasburger claims, 

 they are direct outgrowths of the forward end. The free 

 spermatozoid (Fig. 133, I) is a flattened band, somewhat blunt 



^ Strasburger (11), vol. iv. p. 116. 



