260 



BOTANY 



sclerenchyma. It is this tissue which gives the polished black 

 appearance to the leaf-stalks of such Fenis as Adiantum. 



Scale-leaves. Scale-leaves, with completely suppressed lamina, are 

 not uncommon. These are especially conspicuous in Struthiopteris, 

 where they form, with the persistent bases of the foliage leaves, a 

 complete covering for the rhizome. In many Tree-ferns, and the 

 Marattiacese, the leaf falls away, leaving a clearly marked scar upon 

 the stem. In the Marattiacese the base of the leaf-stalk is provided 

 with large stipules which are usually wanting in Ferns. 



D 



Fro. 225. Adiantum emarginatum. Development of the root. A, longitudinal 

 section of root-apex. B-E, series of transverse sections (x 200) ; z, apical cell; 

 s, s, sextant walls ; en, endodermis. 



Trichomes. The paleee and hairs covering the young parts are 

 undoubtedly protective. Where they develop mucilage-glands, their 

 importance in preventing loss of moisture is sufficiently apparent. 



The Root 



The primary root of the sporophyte is of limited duration, and is 

 soon replaced by others which continue to develop as long as the 

 sporophyte lives. The roots always arise near the base of the leaves, 



