XII 



EQUISETINE^ 



451 



separate lobes. A similar condition exists in Osmuncia, where 

 in the older prothallia similar but much shorter and broader 

 lobes arise alternately from either side of the growing apex. 



The development of the archegonium is intimately associated 

 with the formation of the lobes. The archegonium mother cell 

 is formed close to the base of the young lobe upon the ventral 

 side. By subsequent growth of the tissue between it and the 

 apical meristem, it is subsequently forced to tlie upper side, but 

 its origin is ventral, as in the Ferns. The lobe at whose base 



Fig. 262. — Development of the archegonium. A, Optical section of the very young 

 archegonial meristem, X225; B-E, longitudinal sections of young archegonia, X450; 

 Cj neck canal cell; v, ventral canal cell; o, egg. 



it is borne grows for some time by a definite apical cell, which is 

 very evident in horizontal sections (Fig. 263, C). 



The development of the archegonium most nearly resembles 

 that of the eusporangiate Ferns. Usually, but not always, no 

 basal cell is formed, and the first division in the inner cell sepa- 

 rates the neck canal cell from the central cell. Both neck and 

 ventral canal cells (Fig. 262, E) equal in breadth the central 

 cell, and in this respect are most like the Marattiaceae. The 

 neck canal cell later grows up between the neck cells, but there 

 is usually a space between its summit and the terminal neck 



