152 THE FLOWERING PLANT. 
If one of these spores is allowed to germinate on a damp tile it 
will grow into a small flat green body, from the under side of 
which root-hairs grow out. This is the prothallus or odphyte, 
and on it are borne archegonia and antheridia, not unlike those 
of the moss. The prothallus is somewhat heart-shaped, with 
an anterior notch, and its central part or “cushion” is rather 
thicker than the rest. The archegonia are situated on the 
under side of the cushion, near the notch, and each archegonium 
consists of a short curved neck which projects freely, and a 
venter imbedded in the prothallus and containing an egg-cell. 
The antheridia are minute dome-shaped bodies also placed on 
the under side of the prothallus but situated near its edge and 
further back than the group of archegonia. Within each 
antheridium are developed numerous spiral antherozoids, each 
provided with a number of slender protoplasmic threads which 
are able to propel it in the moisture present on the prothallus. 
As in the moss, fertilization consists in the fusion of a single 
antherozoid with the egg-cell. The fertilized egg-cell or odspore 
grows into a young fern-plant (sporophyte), which remains for 
some time attached to the prothallus and then falls off and 
takes root in the ground. The sporophyte is often able to pro- 
duce fresh sporophytes by vegetative reproduction. 
The life-history of the fern is summarized in the following 
diagram :— 
SPOROPHYTE 
Fern Plant 
Pe 
eporaneim oospore 
| Ye 
spore egg-cell antherozoid 
archegonium antheridium 
—> 
Prothallus 
OOPHYTE 
The sporophytes of ferns differ from one another in various respects, 
such as shape and position of the rhizome, shape of the leaves, &c., 
and, what is of more importance, the arrangement of the sori. In the 
hart’s-tongue (Scolopendrium vulgare), for example, the sori are oblique 
