254 



MOSSES AND FERNS 



CHAP. 



near the foci of the elhptical section. From here the formation 

 proceeds towards the centre, and in the full-grown root the 

 tracheary tissue forms a continuous band occupying the larger 

 axis of the section, the last-formed tracheids being the largest. 

 On either side of this tracheary plate is a poorly defined mass 

 of phloem, similar to that of the stem and leaf bundles. An en- 

 dodermis or bundle sheath can be made out, although it is much 

 less prominent than in most roots. The endodermis is derived 

 from the innermost cortical layer, and the radial cell-walls are 

 characterised by a thickening, or folding of the wall. In O. vul- 



gatitiu the bundle of 

 the root is diarch to 

 begin with, but by the 

 suppression of one of 

 the phloem masses it 

 becomes monarch. 



The Sporangium 



The development 

 of the sporangium has 

 been studied by 

 Goebel ((17), p. 

 390), in O. vidgatmn, 

 and recently by Bower 

 (16) in this species 

 and in 0. pendulum. 

 The latter has been 

 carefully examined by 

 the writer, and the re- 

 ^'°' ii^-"^-/"'/,"'"'"-. \^T\^' ^""'^'f °^ '^" '°°*' suits confirm that of 



X05, Ihe phloem is shaded; en, endodermis. 



the latter investigator, 

 except that it seems possible that the archesporium may be 

 traced to a single cell, as Goebel asserts is probably the case in 

 O. vulgatum. 



According to Bower (16), in all species examined by him, 

 the sporangia arise from a continuous band of superficial tissue, 

 on each side of the spike. To this he gives the name, ''sporan- 

 giogenic band." The sporangia arise from the sporangiogenic 

 band, at more or less definite intervals, separated bv intervals 

 of sterile cells. In the sporangial areas, periclinal walls sep- 



