252 MOSSES AND FERNS CHAP. 



somewhat smaller size of the cells of the bundle itself indeed 

 it is not always easy to say exactly where the ground tissue 

 begins. The xylem is composed of pointed tracheids whose 

 walls are marked with thick reticulate bands. This mass of 

 tracheary tissue is situated near the inner side of the bundle, 

 which like that of the stem is collateral. The rest of the 

 bundle is composed of sieve-tubes mingled irregularly with 

 smaller cambiform cells. Whether or not sieve-tubes occur 

 upon the inner side of the bundle 'could not be positively deter- 

 mined. The sieve-tubes have transverse walls, and in O. vul- 



FIG. 136. Vascular bundle of the petiole of O. pendulum, X26o; t, t, the xylem 



of the bundle. 



gatum lateral sieve-plates have been observed. The spo- 

 rangiophore has much the same anatomical structure as the rest 

 of the leaf, but stomata are quite absent from its epidermis. 

 In this respect 0. pendulum differs from O. vulgatum and 

 allied species, where stomata are developed upon the spo- 

 rangiophore as well as upon the rest of the leaf. 



The Root 



The roots are formed singly near the bases of the leaves, 

 and are light yellowish brown in colour, and so far as could be 



