266 



MOSSES AND FERNS 



CHAP. 



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. 

 Farmer^ figures the cotyledon of Aftgiopteris as more spatulate 

 in form, with a distinct midrib, but this is never the case in 

 M. Douglasii. 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 approaches 

 the collateral form of 

 Op Jiioglossum. I n - 

 deed, if the tannin 

 cells, which are found 

 here, belong to the 

 cortex, as Farmer 

 asserts to be the case 

 Angiopteris, the 



Fig. 138. — Horizontal section of the lamina of the cotyledon of 

 M. Douglasii, X 260. 



m 



bundle would be truly 

 collateral, as these are 

 immediately in contact with the tracheids. The lamina of the 

 cotyledon is similar in structure 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. 



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 

 older parts of the root to the segments of the apical cell is 



^ Farmer (3), Figs. 19-21. 



