49 



growing-point by the decay or arrest of one or more 

 cells, members of a linear series, which occupy a 

 central position in relation to the changes that follow. 

 By this local cessation of growth and the active 

 division of the adjoining cells there is formed, first a 

 short cylindrical canal, and ultimately the flask-shaped 

 or globular cavity. The initial cell either disappears 

 altogether (as in' Himanthalia,), or only the upper 

 portion (as in Salidrys), in which case the middle 

 part gives rise to a hair, while the basal cells share 

 in the formation of the base of the conceptacle. 

 In Ascopkyllum the whole initial cell persists and sub- 

 sequently grows out into the conceptacle forming 

 a sort of placenta. In Notheia, the branches issue 

 from the base of conceptacles (Fig. 5 I), probably 

 owing to the continued development of the initial 

 cell. 



Both hermaphrodite and unisexual conceptacles 

 occur. In those cases in which both oogonia and 

 antheridia are borne within the same conceptacle 

 the oogonia usually occupy the base while the 

 antheridia occur on the sides, but this rule is not 

 constant, and they sometimes occur intermixed. 

 When the conceptacles are unisexual it is usually 

 the case that the different sexes occur on different 

 plants, but not always so, as is sometimes asserted. 



The oogonia originate from two-celled hairs, the 

 lower of which becomes the pedicel and the upper 

 the oogonium proper. The pedicel cell is usually 

 very short, and in some cases is wholly buried in the 

 wall of the conceptacle. While this is the rule, 

 an exception occurs in Sarcophycus, which possesses 



E 



