330 HOFMEISTER, ON 



formation of the first archegonium — the three lobes of the 

 outer spore-membrane* are bent back. 



The formation of the subsequent archegonia, which appear 

 in numbers upon the prothallium, takes place in a similar 

 manner by transverse division of one of the cells of the outer 

 surface of the prothallium. The central cell is formed from 

 the inner of the daughter-cells, whilst from the outer ones 

 are produced the boundary cells of the canal leading to the 

 central cell. After the formation of those archegonia, which 

 are situated near the highest of the three blunt angles of 

 the three-sided, cushion-shaped prothallium, transverse divi- 

 sion is sometimes several times repeated in the covering 

 cells of the archegonia, and in the tissue surrounding them. 

 The canal leading to the central cell of these latter arche- 

 gonia is of considerable length, and has a bent course (PL 

 XLV, fig. 10). 



At the commencement of the formation of the archego- 

 nium the central cell is quite filled with granular mucilage, 

 and a nucleus with more transparent contents floats in the 

 middle of it (PI. XLV, fig. 5). Afterwards, as the central 

 cell increases in size, the granular protoplasm accumulates 

 so as to cover the wall, and the nucleus is imbedded in it. 

 One or two oval or pear-shaped cells, in contact with the 

 inner wall, are now visible in the upper arch of the cell : 

 these are the germinal vesicles (PI. XLV, figs. 6 — 9). They 

 not unfrequently occur in pah's, a fact not hitherto observed 

 in any other vascular cryptogam. 



During these changes in the large spores, the sporangia 

 which contain small spores are also carried up to the surface 

 of the water, either in groups or singly. In autumn, when 

 the mother-plant dies, the small spores contained in each 

 ripe sporangium are firmly attached to one another and not 

 capable of isolation, their outlines being hardly distinguish- 

 able. This has been observed by Mettenius,f and the same 

 is the case even in early spring. If however such a spo- 

 rangium be subjected at this time to gentle pressure under 



* The two glassy inner layers remain during this process, as during the 

 entire act of germination, quite unchanged (PI. XLV, fig. 2). The notion of 

 their conversion into an apparently cellular mass is erroneous. (Mettenius 

 ' Beitr. z. K. d. Rhizocarpeen, 5 p. 17.) 



f 'Beitr. zur K. der Rhizocarpese. 5 Frankfort, a. M., 1846, p. 19. 



