278 MOSSES AND FERNS chap. 



detached and form independent plants; or they may develop 

 sexual organs (mainly antheridia) while still connected with 

 the mother plant. The duration of the prothallium is apparently 

 unlimited, so long as it remains un fecundated. The writer 

 kept prothallia of Marattia Douglasii 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 

 midril). Both antheridia and archegonia resemble closely those 

 of Ophioglossum. 



The Sex-organs 



The antheridium arises from a single superficial cell which 

 first divides into an inner cell, from w^hich the sperm cells are 

 derived, and an outer cover cell (Fig. 152, A). The latter 

 divides by several curved vertical walls (Figs. E-G) Avhich 

 intersect, and the last wall cuts off a small triangular cell (o), 

 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 comi)letely 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 spermatozoid, stains strongly with alum-cochineal, and 

 is sharply differentiated against the colourless cytoplasm, and 



