328 MOSSES AND FERNS' chap. 



Most of the Leptosporangiatae are characterised by numer- 

 ous epidermal outgrowths, either hairs or scales. These are 

 especially abundant upon the younger parts, and are largely 

 protective. The hairs are either simple or glandular ones. In 

 the latter case the gland is usually a terminal, pear-shaped cell, 

 which secretes mucilaginous matter, or less frequently {Onoclea 

 strutJiiopteris) this secretion may be resinous. In the common 

 Californian " gold-back " Fern, Gymnograninie triangularis, the 

 yellow powder upon the back of the leaf is a waxy secretion, 

 derived from epidermal hairs. Of similar nature are the large 

 chaffy scales (palese) which occur in such numbers upon the 

 bases of the petioles of so many Ferns. This development of 

 hairs, however, is most marked in the large tree-Ferns, Dicksonia, 

 Cibotiuin, etc., where the young leaves are completely buried in 

 a thick mass of brown wool-like hairs, which are sometimes 

 utilised as a substitute for wool in stuffing mattresses, etc. 



The Root 



The roots arise in large numbers in most Ferns, and 

 apparently bear no definite relation to the leaves. The primary 

 ones are first visible very near the apex of the stem (Fig. 162, 

 A, r), and Van Tieghem,^ who has made a very exhaustive study 

 of the subject, states that they always arise from an endodermal 

 cell. This divides into a basal cell and a terminal one, and by 

 the former the young root is directly connected with the xylem 

 of the stem bundle. In the outer cell the three walls defining 

 the pyramidal apical cell now arise, and the latter at once 

 begins its characteristic divisions. 



The segmentation in the apex of the roots of the Lepto- 

 sporangiatae is exceedingly regular. Corresponding to each 

 set of lateral segments an outer segment forms as well. Van 

 Tieghem " does not apparently recognise the root-cap as distinct 

 from the epidermis, but all other observers consider the root- 

 cap as a distinct structure. The first division wall in the lateral 

 segments is the sextant wall, which is perpendicular to the broad 

 faces of the segment and curves somewhat so as to strike one of 

 the lateral walls a little above the base, and thus makes the two 

 sextant cells of unequal size (Fig. 165, C). The next wall is 

 transverse and separates an inner from an outer cell, and with 

 ^ Van Tieghem (5). - Van Tieghem, I.e. 



