446 



BOTANY 



whole, and to the Water-Ferns. Unlike the leaves of Phanerogams, those of 

 the Ferns continue to grow at the apex until their full size is attained. The 

 leaves of the common Polypodium vulgare are pinnate, and spring singly from 

 the upper side of the branched rhizome, which creeps amongst Moss or on rocks. 

 In other cases the leaves may be simple and undivided, as in the Hart's-Tongue 



FKJ. 406. Alsophila crinita. A Tree-Fern growing in Ceylon. (Reduced.) 



Fern, Scolopendrium vulgare (Fig. 408). In the tropics many herbaceous Ferns 

 grow as epiphytes on forest trees. 



Peculiar brownish scales (paleae, ramenta), often fringed and consisting of a 

 single layer of cells, invest the stems, petioles, and sometimes also the leaves of 

 most' Ferns. These are morphologically trichomes. 



The sporangia are generally produced in large numbers, on the under side of 

 the leaves. The sporophylls, as a rule, resemble the sterile, foliage leaves. In a 

 few genera a pronounced heterophylly is exhibited : thus, in the Ostrich Fern, 

 Struthiopteris gennanica (Onoclea- Struthiopteris), the dark brown sporophylls are 



