^86 MOSSES AND FERNS CHAP. 



primary vascular axis is a simple concentric stele, which is later 

 replaced by a cylindrical stele like that of D. data. 



Short hairs with cells rich in tannin, and staining strongly 

 with Bismarck-brown, occur sparingly upon the leaves and 

 stem of the young sporophyte. 



The fully-developed cotyledon has the fan-shaped lamina 

 somewhat lobed, and the two primary veins arising from the 

 forking of the original vascular bundle usually fork once more, 

 so that the venation is strictly dichotomous in character. The 

 nearly cylindrical petiole is deeply channeled upon the inner 

 side, and the single axial vascular bundle is almost circular in 

 section. While the crescent-shaped mass of tracheary tissue is 

 completely surrounded by the phloem, the latter is much more 



strongly developed 

 upon the outer side, 

 and the bundle ap- 

 proaches the collateral 

 form of Ophioglos- 

 sum. Indeed, if the 

 tannin cells, which are 

 found here, belong to 

 the cortex, as Farmer 

 asserts to be the case 

 in Angiopteris, the 

 bundle would be truly 



FIG. ^.-Horizontal section of the lamina of the Collateral, as these tail- 

 cotyledon of M. Dougiasii, X26o. nin cells are immedi- 

 ately in contact with 



the tracheids. The lamina of the cotyledon is similar in struc- 

 ture to that of the later leaves, and differs mainly in the smaller 

 development of the mesophyll. The smaller veins have the 

 xylem reduced to a few (1-3) rows of tracheids upon the 

 upper side of the collateral bundle. Stomata of the ordinary 

 form occur upon the lower side of the leaf. 



In Angiopteris (Fig. 157, C) and Dancca (Fig. 157, A), 

 the cotyledon is spatulate in outline with a distinct midrib. 



As the root finally breaks through the calyptra and pene- 

 trates into the earth, numerous fine unicellular root-hairs 

 develop from the older parts, but the tip for some distance 

 remains free from them. Owing to the numerous irregularities 

 in the cell divisions, the exact relation of the tissues of the 



