vii PTERIDOPHYTA—FILICINEAl—OPHIOGLOSSACEAi 269 



point, but the youngest stages found by me in which the 

 sporangial nature of the outgrowths was unmistakable, would 

 not forbid such an interpretation, although there was no doubt 

 that the basal part of the sporangium is derived in part from the 

 surrounding tissue. 



From the central cell, by a periclinal wall, an inner cell, 

 the archesporium, is separated from an outer one. The outer 

 cell divides next by cross w^alls, and this is followed by similar 

 divisions in the inner cells (Fig. 148). The succeeding divi- 



FiG. 148. — Botrychium Virginianum. Development of the sporangia. A, i, 2, 

 Very young sporangia; B, a somewhat older one, X480; C, older sporangium, 

 X240; all median longitudinal sections, the sporogenous cells are shaded. 



sions in the outer cells are now mainly periclinal, and transform 

 the four cells lying immediately above the archesporium into 

 as many rows of tabular cells. Growth is active in the mean- 

 time in the basal part of the sporangium, which projects more 

 and more until it becomes almost spherical. To judge from 

 the account given by Goebel (3) and Bower (16) of B. lunaria, 

 this species corresponds closely in its early stages to B. Vir- 

 ginianum. The later divisions in the archesporium do not 

 apparently follow any definite rule, but divisions take place 

 in all directions until a very large number of cells is formed. 



