FILICINEM. 



w 



Like many thalloid Hepaticae, the prothallia of Ferns also produce adventitious 

 loots from single marginal cells ^; this happens with especial profusion in Osmunda, 

 rhere the adventitious shoots become detached, and play the part of vegetative 

 >rgans of reproduction. 



The prothallia show a tendency to be dioecious, which is manifested in the 

 ict that all the spores from a sporangium sometimes produce prothallia bearing 

 ^ntheridia only (as in Osmunda regaJis) ; while in other cases the archegonia 

 Appear later and in smaller numbers, and are fertilised by the antheridia of younger 

 prothallia. 



The Antheridia are, speaking morphologically, trichomes ; they are produced in 



le same manner as the root-hairs, as outgrowths of the marginal or superficial cells 



^f the prothallia ; in the Hymenophyllacese they are also produced on the protonemal 



ilaments. The projection is usually separated from the mother-cell by a septum, 



ind swells up spherically at once or after the formation of a pedicel. In some 



:ases the mother-cells of the antherozoids are formed at once in this globular cell ; 



)ut it usually undergoes still further divisions^, in consequence of which the wall of 



le antheridium consists of a single layer of cells surrounding the central cell. 



''ithin the cells of this layer chlorophyll-granules are formed towards their inner wall, 



rhile the central cell of the antheridium divides further into the mother-cells of the 



mtherozoids, which, however, are not numerous. The dehiscence of the ripe anthe- 



idium is the consequence of a rapid absorption of water in the parietal cells, which 



swell up violently and compress the contents of the central cell till the antheridium is 



ruptured at the apex. The antherozoid-cells thus escape, and out of each of them 



is set free an antherozoid coiled spirally three or four times. The finer anterior end 



)f each antherozoid is provided with a number of cilia ; the thicker posterior end 



>ften drags with it a vesicle furnished with colourless granules, which subsequently 



Falls off and remains at rest, while the filament alone continues in motion. Stras- 



mrger states that this vesicle is formed from a central part of the contents of the 



lother-cell, the parietal protoplasm of which forms the filament and its cilia. The 



vesicle is hence properly not a part of the antherozoid; it is only attached to it, 



ind swells up strongly in water by endosmose, as is shown in Fig. 293. 



The Archegonium arises from a single superficial cell of the prothallium, which 

 is at first only slightly arched and is divided by two walls parallel to the upper 



* [On the formation of gemmae by Fern-prothallia, see Cramer, Ueb. geschlechtslose Vermehrung 

 ies Farn-pro thallium, Basel 1881.] 



^ These divisions take place in a very remarkable manner. In the hemispherical mother-cell of 

 the antheridium of Aneimia hirta an arched vi'all arises, by which it is divided into an inner hemi- 

 spherical cell, and an outer one which covers the former like a bell ; the latter is then split up by a 

 transverse annular wall into an upper lid-like and a lower hollow cylindrical cell. The same thing 

 ;curs in Ceratopteris ; in other cases, as in Asplenium alatum, a funnel-shaped wall is formed in 

 le hemispherical mother- cell of the antheridium, the wide end of the funnel being directed towards 

 le upper surface of the mother-cell, and the upper part of the mother-cell is cut off by a transverse 

 ;ptum as a covering cell ; two, or even three, funnel-shaped walls may be formed in succession, so 

 lat the parietal layer of the antheridium consists of two or three superposed cells forming its 

 Jircumference and a covering cell (as in Fig. 293). The mode of formation of the antheridium-wall 

 quite different in Osmunda, where it consists below of two or three cells, upon which rest several 

 >f the upper cells which result from the division of the covering cell (Kny, /. c). — [See also Stras- 

 nirger, Theilungsvorgange in den Antheridicn der Fame; Zcllbildung und Zeltthcilung, 3rd edition.] 



