235 



Fig. 153. 



lipilillioii inenili (iiidceii/ji. vertical, somewhat excentric 

 section of sporangial coiiceptacle. IM.5:1. 



cells of the basal layer situated at the periphery of the conceptacle lengthen in a 

 vertical direction, fuse laterally two or three together, and are finally disorganized, 

 the upper part of their membrane being 

 dissolved as far as it meets the cavity of 

 the conceptacle. The cells of the same 

 layer forming the central part of the floor 

 of the conceptacle are disorganized in the 

 same way, their contents finally disappearing, 

 but they do not lengthen. In fig. 152 1) the 

 contents of these cells are still visible. In 

 the sexual conceptacles the basal layer is 

 exhausted in a similar way. The formation 

 of the three dividing walls of the sporangia 

 is almost simultaneous, the walls advancing slowly from the periphery towards the 

 longitudinal axis of the sporangium (fig. 152 B, D). 



The antheridial conceptacles were found agreeing with the description and 

 figure of RosANOFF (1. c. p. 59, pi. II fig. 14). The cells surrounding the orifice are 

 elongated and directed obliquely upwards (fig. 154). The antheridia clothe the bottom 

 of the conceptacle; their development and structure have been followed by Guignahd, 

 who found that they are seriate in densely placed short filaments. When the sper- 

 matia are to be formed, the protoplasm accumulates around the nucleus in the 

 middle of the cell and becomes surrounded by a thin membrane, while the rest of 

 the contents develop into two appendices, first described by Rosanoff and named 

 "oreillettes". 



The orifice of the cystocarpic conceptacles is clothed with similar elongated, 

 hair-shaped cells like those of the antheridial conceptacles, but more numerous; 

 they are directed inwards or downwards in the under part, upwards in the upper 

 part of the orifice. The carpospores are only produced at the periphery of the 

 conceptacle; in the central part of the floor carpogonia are still visible, when the 

 carpospores are well developed (fig. 155 B). As to the structure of the procarps I 



cannot give any certain 

 statement; they seem to 

 resemble those of Litho- 

 thninnion polymorpluim. 



The species, referred 

 by earlier authors to the 

 genus Melobesia, had been 

 transferred by Heydrich 

 in 1897 to a new genus 

 Epilithon, which was re- 

 duced in the following year by Foslie to a subgenus of Lithothamnion, with which 

 it agrees by the fructification. The want of diflferentiation in hypothallium and 



30* 



Fig. 154. 



lipilitlwn ini'iiitir<inacciiiii, vertical section of antheridial conceptacle. 5(K):1. 



