PTERIDOPHYTA. 203 
number of spores. The hairs are thus spore-cases. In 
some ferns these clusters of spore-cases are naked (Fig. 113, 
A), while in others they are covered by a special outgrowth 
of the epidermis (Fig. 1138, B, C), or by a folding of a 
part of the leaf (Fig. 113, D), ete. 
427. The mature spore-case in most common ferns has a 
ring of thicker cells extending around it. When these 
become dry, they contract in such a way as to break open 
the spore-case and thus set the spores free. 
428. The spores soon germinate, upon moist earth. The 
first stage thus produced is generally a little heart-shaped, 
flat, green plant, adhering closely to the earth by its root- 
hairs. After some weeks or months little “seedling” ferns 
may be found, with one or two minute leaves. Under 
favorable conditions every such fernlet will give rise to a 
strong and long-lived fern. 
Among our common ferns are the Common Polypody (Polypodium 
vulgare, Fig. 112), the Golden Fern (Gymnogramme triangularis) of 
California, the Maidenhair of the North (Adiantum pedatum) and of 
the South (A. capillus-veneris), the Common Brake (Pteris aquilina), 
the Spleenworts (Asplenium) of many species, the Shield-ferns (Aspi- 
dium), also of many species, the curious little Walking-leaf (Campto- 
sorus rhizophyllus), the Bladder-fern (Cystopteris fragilis), the large 
Ostrich-fern (Onoclea struthiopteris), the Flowering Ferns (Osmun- 
da) of several species, and, most beautiful of all, the Climbing Fern 
(Lygodium palmatum) of the Appalachian region. 
In the Coal Period the ferns were much more numerous than at 
the present. Many families which flourished then are now extinct. 
The ferns of that period were often tree-like and of large size. 
429, The Ringless Ferns (Order Marattiacew) constitute 
an interesting transitional group, all exotics. Some are 
cultivated in fern-houses. 
430. The Adder-Tongues ( Order Ophioglossacee) include 
a few species of fern-like plants, which differ from the true 
