PHAOPHYCEA 105 
possess no definite growing point. The reproductive 
organs are both unilocular and plurilocular sporangia 
arising by the differentiation of a superficial cell or 
of an outgrowth from one. The conjugation of 
gametes has been observed in one form. 
The Thallus in the filamentous form is articulated, 
and consists of several rows of cells, but sometimes 
partially or even wholly of a single row. However, 
most of the forms exhibit both a cortical tissue and 
an internal one. The internal tissue consists of large 
parenchymatous cells, and the cortical layer of smaller 
assimilative cells, though these are commonly of 
relatively greater size than in allied groups. Hairs 
and paraphyses sometimes spring from the super- 
ficial cells, the hairs with basal growth (at least in 
the case of Punctaria, and more notably Hydrocla- 
thrus) from pits resembling cryptostomata of simple 
structure. The attachment of the thallus to the 
substratum is either by means of a disc or by a weft 
of rhizoids. Immediately above the attachment the 
base of the thallus is commonly attenuated to a thin, 
solid and short stalk. There is no true growing point, 
and the growth is distributed more or less equally 
over the whole thallus, but persists at the base, as a 
rule, for a time after it has ceased elsewhere. The 
development of the cryptostomata has been observed 
in Hydroclathrus. Ina surface view “an isolated cell 
or several cells in a group become separated off from 
the surrounding epidermis, each loses its polygonal 
shape and becomes cylindrical. . . . In a radial sec- 
tion of such a group each cell is seen to be divided 
by a transverse wall, but there is no indication of 
