FILICINEM. 
Like many thalloid Hepaticse, the prothallia of Ferns also produce adventitious 
shoots from single marginal cells ^; this happens with especial profusion in Osmunda, 
where the adventitious shoots become detached, and play the part of vegetative 
organs of reproduction. 
The prothallia show a tendency to be dioecious, which is manifested in the 
fact that all the spores from a sporangium sometimes produce prothallia bearing 
antheridia only (as in Osmimda regalis) ; 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 
the same manner as the root-hairs, as outgrowths of the marginal or superficial cells 
of the prothallia ; in the Hymenophyllacese they are also produced on the protonemal 
filaments. The projection is usually separated from the mother-cell by a septum, 
and swells up spherically at once or after the formation of a pedicel. In some 
cases the mother-cells of the antherozoids are formed at once in this globular cell ; 
but it usually undergoes still further divisions^, in consequence of which the wall of 
the antheridium consists of a single layer of cells surrounding the central cell. 
Within the cells of this layer chlorophyll-granules are formed towards their inner wall, 
while the central cell of the antheridium divides further into the mother-cells of the 
antherozoids, which, however, are not numerous. The dehiscence of the ripe anthe- 
ridium 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 
of each antherozoid is provided with a number of cilia ; the thicker posterior end 
often 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- 
burger states that this vesicle is formed from a central part of the contents of the 
mother-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, 
and svi^ells up strongly in water by endosmose, as is shown in Fig. 293. 
The Archegoniiivi arises from a single superficial cell of the pro thallium, 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 
des Farn-prothallium, Basel 1881.] 
^ These divisions take place in a very remarkable manner. In the hemispherical mother-cell of 
the antheridium of Aneimia hirta an arched v^-all arises, by which it is divided into an inner hemi- 
spherical cell, and an outer one vi^hich 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 
occurs in Ceratopterh; in other cases, as in Asplefiium alatiim, a funnel-shaped wall is formed in 
the hemispherical mother- cell of the antheridium, the wide end of the funnel being directed towards 
the upper surface of the mother-cell, and the upper part of the mother-cell is cut off by a transverse 
septum as a covering cell ; two, or even three, funnel-shaped walls may be formed in succession, so 
that the parietal layer of the antheridium consists of two or three superposed cells forming its 
circumference and a covering cell (as in Fig. 293). The mode of formation of the antheridium-wall 
is quite different in Osmunda, where it consists below of two or three cells, upon which rest several 
of the upper cells which result from the division of the covering cell (Kny, c.).— [See also Stras- 
burger, Theilungsvorgänge in den Anlheridien der Farne ; Zellbildung und Zelltheilung, 3rd edition.] 
