250 MOSSES AND FERNS chap. 



The Sporangium 



In the simplest forms of B. simplex the sporangia, which 

 are much larger than those of B. Virginianum, form two rows 

 very much as in Ophioglossmn ; but in all the more complicated 

 forms the sporangiophore branches in much the same way as 

 the sterile part of the leaf, and the ultimate segments become 

 the sporangia. In B. Virginianum the development of the 

 individual sporangia begins just about a year previous to their 

 ripening, and if the plants are taken up about the time the 

 spores are shed, the earliest stages may be found. The 

 sporangiophore is at this time thrice pinnate in the larger 

 specimens, and an examination of its ultimate divisions will 

 show the youngest recognisable sporangia. These form slight 

 elevations growing smaller toward the end of the segment 

 (Fig. 129), and exact median sections show that at the apex of 

 the broadly conical prominence which is the first stage of the 

 young sporangium there is a large pyramidal cell with a 

 truncate apex. Holtzman -^ thinks the sporangium may be 

 traceable to a single cell, and that the divisions at first are like 

 those in a three -sided apical cell. I was unable to satisfy 

 myself on this 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 walls, and this is followed by similar 

 divisions in the inner cells (Fig. 129). The succeeding divi- 

 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 

 meantime in the basal part of the sporangium, which projects 

 more and more until it becomes almost spherical. To judge 

 from the somewhat incomplete account given by Goebel ^ of 

 B. lunaria, this species corresponds closely in its early stages 

 to that of B. Virginianum. The later divisions in the arche- 

 sporium do not apparently follow any definite rule, but divi- 



1 Holtzman (i). ^ Goebel (3). 



