PHAOPHYCEA 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 cylindrica] canal, and ultimately the flask-shaped 
or globular cavity. The initia! cell either disappears 
altogether (as in Himanthalia), or only the upper 
portion (as in Halidrys), in which case the middle 
part gives rise toa hair, while the basal cells share 
in the formation of the base of the conceptacle. 
In Ascophyllum 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 6), 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 
