ADIAXTTM Fl-DATl'M. 125 



As the cap is gradually disorganized and worn away by 

 contact with the soil it is replaced by new growth from 

 behind. The root cap is to be considered as a modified 

 and augmented portion of the epidermis. 16 



Provision for continued growth of the stem in 

 length is found in the bud at its apex. The dying 

 base, however, follows with equal pace the advancing 

 apex, severing the lateral branches as it reaches them, 

 which thus become independent plants. 



One of the most marked advances upon the structure 

 of the moss is to be found in "the development of an 

 extensive and complicated fibro-vascular system. The 

 simple leaf traces of Atrichum are here replaced by 

 better developed groups of fibers and vessels to which 

 the term fibro-vascular bundle is applied. These 

 bundles are distributed to every part of the plant ; con- 

 densed in those parts requiring strength, such as the 

 roots, stem and leafstalk ; diffusely branched in the 

 leaflets for the support of the chlorophyll-bearing 

 tissue. Branches of the fibro-vascular bundles having 

 once been formed, do not reunite with their fellows, 

 either as a whole or by anastomosing branchlets. The 

 only organs of Adiantum not reached by the fibro- 

 vascular bundles are the numerous and unusually 

 varied trichomes. These are developed as scales 

 thickly clothing the stem and base of the leaf stalk, as 

 hairs matted together about the roots, and as sporan- 

 gia crowded under the edges of the leaflets. 



In the growing parts of all organs of the fern, the 

 cells are parenchymatous, but certain groups early dif- 



16 Bessey, Botany, p. 163. 



