FUCALES (HETEROGENERATAE) 195 



became overgrown by the surrounding tissue. This has since been 

 abandoned. 



(2) According to the second account a linear series of two or more 

 cells is formed but their horizontal activity then ceases, thus leaving 

 a terminal initial cell which becomes sunk in a depression as the 

 surrounding tissues grow up. On this theory the sides of the con- 

 ceptacle are derived from the limiting layer and underlying cortex, 

 as Bower (1880) demonstrated for Fucus, whilst in Himanthalia the 



o c 



Fig. 130. Fucus. A-C, origin of conceptacles in F. serratus. 6 = basal cell, 

 z = initial. D, juvenile conceptacle of Cystoseira. /i = hair. (After Oltmanns.) 



sides are derived from the limiting layer only. Finally, around the 

 remnants of the one or more initial cells a central mucilaginous 

 column is formed stretching to the neck of the conceptacle and 

 connected to the walls by thin strings of mucilage which are later 

 ruptured. According to this description, therefore, the conceptacles 

 are the products of one or more initials which may or may not 

 disintegrate at a later stage (cf. fig. 130). 



(3) The third account describes the conceptacle as developed 

 entirely from a single initial that divides transversely into two un- 

 equal cells, the upper or tongue cell degenerating whilst the lower 



13-2 



