PTMBIDOPHTTA. 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. 113, S, G), or by a folding of a 

 part of the leaf (Fig. 113, J)), etc. 



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 f ernlet will give rise to a 

 strong and long-lived fern. 



Among our common ferns are the Common Polypody (Polypodium 

 Tulgare, Fig. 113), tjie Golden F§rn (G-ymnogramme triangularis) of 

 California, the Maidenhair of the North (Adiantum pedatum) and of 

 the South (A. capillus-veneris), the Common Brake (Pteris aquilina), 

 the Splcenworts (Asplenium) of many species, the Shield-ferns (Aspi- 

 dium), also of many species, the curious little Walking-leaf (Oampto- 

 sorus rhizophyllus), the Bladder-fern (Cystopteris fragilis), the large 

 Ostrich-fern (Onoclea struthiopteris), the Flowering Perns (Osmun- 

 da) of several species, and, most beautiful of all, the Climbing Pern 

 (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 MarattiaceoB) constitute 

 an interesting transitional grojip, all exotics. Some are 

 cultivated in fern-houses. 



430. The Adder-Tongues ( (9r6?e»* Ophioglossacem) include 

 a few species of fern-like plants, which differ from the true 



