(figs. 830 and 832). Upon the under 
: surface of this structure we have soon 
_ formed, in most of the Filices, both 
 antheridia and archegonia; but in 
_ some, as well as usually in the Equi- 
setaceve, the antheridia and archegonia 
have only been found on separate pro- 
_ thallia, and hence the latter plants are 
dicecious. The antheridia (fig. 807) 
contain a number of minute cells called 
sperm-cells (se), each of which contains 
a spirally wound ciliated antherozoid 
(sp). The archegonium (fig. 808) is a 
little cellular papilla, having a central 
canal, which when mature is open. 
At the bottom of the canal is a cell 
called the embryo-sac, in which a germ 
or embryo-cell is developed. This so- 
called embryo-cell is, however, simply 
a germinal corpuscle till after fertilisa- 
tion; that is, a free primordial cell, 
or mass of protoplasm without an ex- 
ternal wall of cellulose. 
When mature, the upper part of 
the antheridium separates from the 
lower, something like the lid of a box ; 
REPRODUCTION OF FILICES AND EQUISETACEA. 835 
In germination, which has also been noticed (pages 366 and 
368), these spores ultimately form a thin, flat, green parenchyma- 
tous expansion or prothallium (jigs. 806 and 1158, p, »), which 
somewhat resembles the permanent thallus of the Hepaticacee 
Bre. L158: 
Fig 1158. Adiantum Cupiilus- 
Veneris. The prothal ium, p, p, 
seen from below, with young 
Fern (sporophore) attached to 
it. 06. Its first leaf. w’', w’, 
Its first and second roots. fA, 
Root hairs of the prothallium 
(x about 30). (After Sachs. ) 
the sperm-cells then escape become raptured, and emit their 
contained antherozoids These antherozoids make their way 
down the canal of the archegonium to the embryo-sac, by which 
the contained gerininal corpuscle is fertilised. This germ-cell 
then developes a pseudo-embryo, which soon possesses rudi- 
mentary leaves and roots (fig. 1158), and ultimately produces 
a plant with fronds bearing sporangia, which resembles the 
parent from which the spore was originally obtained. The 
Ferns and Horsetails are thus seen to exhibit two stages of 
existence : in the first, the spores produce a thalloid expansion ; 
and in the second, by means of antheridia and archegonia upon 
the under surface of this prothallium, 
there is ultimately pro- 
duced anew plant, resembling in every respect the one from 
which the spore was originally derived. Hence Ferns and 
Horsetails exhibit what has been termed alternation of genera- 
tions. 
Two remarkable conditions have been found to obtain in 
certain Ferns with regard to their method of reproduction. Thus 
in Pteris cretica, although antherozoids are developed, no arche- 
Bio! 4 
