KEPRODUCTIVE ORGANS OF EQUISETACEA. 367 
‘the antherozoid, which performs the same function as the pollen 
of flowering plants. The archegonia (fig. 808) are little cellular 
papille of a somewhat oval form, with a canal in their centre 
leading to a cavity which has been called the embryo-sac, and in 
which, before impregnation, is a cell termed the germ-cell or 
Fig. 808. Fic. 809. 
Fig. 808. Vertical section of an archegonium, 
passing through the canal and embryo-sac, 
After Henfrey.— Fig. 809. Prothallium, p, p, 
of Adiantum Capilius-Veneris seen from below, 
showing the Fern-plant developed from the fer- 
tilised germ-cell of the archegonium. 06, First 
frond. uw,’ wv.” Roots. A. Root-hairs, After 
Sachs. 
germ-corpuscle. Impregnation takes place by the contact of the 
antherozoids with the germ-corpuscle, and from the development 
of this, after fertilisation, ultimately the plant with fronds bear- 
ing sporangia is produced (jig. 809). 
The Ferns are thus seen to exhibit in their growth two 
generations : in the first of which the spore produces a thalloid 
expansion, with antheridia and archegonia—the prothalliwm or 
sexual generation ; and in the second, a new plant resembling 
the one from which the spore was originally derived—the ase.wal 
or non-sexual generation (sporophore) or Fern proper. Thus, 
Ferns exhibit an instance of what has been called alternation of 
generations. 
In some rare cases, as in Pteris cretica, no archegonia are 
produced, although the antheridia are fully developed. The 
Fern proper then arises from the prothallium in a simply vege- 
tative manner ; this is known as apogamy. 
2. EQuiseracE& or Horseraits.—In these plants the fully 
developed fructification, found usually in the early spring, is 
borne in cone-like or club-shaped masses at the termination of 
the stem-like branches (fig. 13). Each mass is composed of a 
number of peltate stalked scales, on the under surface of which 
numerous spore-cases, called sporangia, or capsules, are arranged 
(fig. 810). These capsules, when ripe, open by a longitudinal 
fissure on their inner surface, and thus set free the contained 
spores. 
