236 



'MOSSES AND FERNS 



CHAP. 



segments. Each of the latter is first divided by a nearly 

 vertical wall, perpendicular to its broad faces, into two " sextant 

 cells," but beyond this no regularity could be discovered in the 

 order of division in the segments, and the tissue at the growing 

 point, especially in longitudinal section, presents a very confused 

 arrangement of the cells. A little lower down two regions are 

 discernible, a central cylinder (plerome), whose limits are not 

 very clearly defined, and the periblem or cortex. A definite 

 epidermis is not distinguishable. 



The first permanent tissue in the plerome cylinder, which 



is elliptical in section, 

 arises in the form of 

 small tracheids near the 

 foci of the elliptical sec- 

 tion. From here the 

 formation proceeds to- 

 wards the centre, and in 

 the full-grown root the 

 tracheary tissue forms a 

 continuous band occupy- 

 ing the larger axis of 

 the section, the last- 

 formed tracheids being 

 the largest. On either 

 side of this tracheary 

 plate is a poorly de- 

 fined mass of phloem, 

 similar to that of the 

 stem and leaf bundles. 

 Here also no bundle- 



FiG. iig. — Vascular bundle of the root of C /^«(^?i:/z«;z, X85. shcath IS prCSCnt and 



the limits of the bundle 

 are not clearly defined. In O. vulgatum the bundle of the root 

 is diarch to begin with, but by the suppression of one of the 

 phloem masses it becomes monarch. 



The development of the sporangium has been studied by 

 Goebel ^ in O. vulgatum, and recently by Bower ^ in this species 

 and in 0. penduhcm. The latter has been carefully examined 

 by the writer, and the results confirm that of the latter investi- 

 gator, except that it seems possible that the archesporium may 

 1 Goebel (17), p. 390. ^ Bower (14). 



