352 



MOSSES AND FERNS 



CHAP. 



The Mature SporopJiyte 



The growth of the stem in the mature sporophyte is only 

 known in O. regalis} Here there is usually an apical cell of 



the same type as that 

 found in the Ophioglos- 

 saceae or Polypodiacese, 

 but Bower ^ states that 

 sometimes it is impossible 

 to refer the tissues to the 

 division of a single initial 

 cell, and that there are 

 probably in these cases 

 several initials. The 

 growth of the stem is 

 much like that in the 

 other Ferns described, 

 and the structure of the 

 older parts shows much 

 the same arrangement of 

 the tissues as that in 

 the typical Polypodiaceae. 

 The vascular bundles, 

 however, are very de- 

 cidedly collateral in struc- 

 ture. A cross-section of 

 the stem (Fig. i8i, B) 

 shows a circle of horse- 

 shoe shaped or wedge- 

 shaped bundles, with the 

 xylem directed inward 

 and bordering directly 

 upon the pith. Between 

 the bundles are layers of 

 parenchyma (medullary 

 rays), and the phloem 

 forms a continuous band 

 outside the woody 

 bundles and bounded externally by the endodermis. The 

 ground tissue is mainly composed of dark sclerenchyma, 

 ^ Bower (ii). ^ Bower, I.e. 



Fig. i8i. — Upper part of a sporophyll of O. Claytoniana, 

 X2 ; sp, sporangia; B, section of the rhizome of O. 

 regalis (L.), showing the arrangement of the vascular 

 bundles, X 4 (after De Barj')- 



