294 



MOSSES AND FERNS 



CHAP. 



hypodermal cell in the axis of the young sporangium. This 

 cell divides repeatedly, but apparently without any definite 

 order, and the division of the spores follows in the usual way. 

 From the cells about the archesporium tapetal cells are cut off, 

 but these do not disappear, as Goebel (3) asserts, but persist 

 until the sporangium is mature. The growth is greater 



upon the outer side, which is 

 strongly convex, while the 

 inner face is nearly flat. 



A section of the nearly 

 full-grown sporangium ( Fig. 

 164, C) shows that the wall 

 upon the outer side is much 

 thicker, and is composed for 

 the most part of three layers 

 of cells, of which the outer 

 in the ripe sporangium have 

 their outer walls strongly 

 thickened. The top of the 

 sporangium and the inner 

 wall are composed of but one 

 layer of cells (exclusive of 

 the tapetum), w r hich are flat 

 and more delicate than those 

 upon the outer side. Near 

 the top on its outer side is a 

 transverse line of cells with 

 thickened darker walls, which 

 project somewhat above the 

 level of the others. This is 

 the annulus or ring, and re- 



FIG. 165. Marattia fraxinea. A, Transverse . _ 



. section of young synangium, X22 5 ; B, SCmbleS Closely that Ot US- 



similar section of ' an older synangium, mun ^a. Lining the Wall IS a 

 Xii2; x, x, the tapetal cells. (After . 



Bower.) layer of very large thin- 



walled cells which form the 



tapetum. This in Angiopteris remains intact until the spores 

 are divided. Whether it disappears before the dehiscence of 

 the sporangium was not determined. The contents of these 

 cells, which are very much distended, and evidently actively 

 concerned in the growth of the forming spores, contain very 

 few granules, but are multinucleate in many cases. Whether 



