98 SEAWEEDS 
DicTYOSIPHONACEZ. 
General Characters.—This group is not well defined, 
but will possibly gain in this respect from future 
investigation. The thallus is of medium stature, of 
two layers of parenchymatous tissue, and grows in 
length by an apical cell. Only unilocular sporangia 
are known. 
The Thallus is attached to its substratum by a 
dense weft of root-hairs, and consists of a loosely con- 
nected internal tissue of elongated cells, attached to 
each other, mostly by lateral processes, and diminish- 
ing in length towards the outside, where this tissue 
merges into the cortical layer. It eventually becomes 
hollow in nearly all cases. The outer cortical layer of 
Dictyosiphon is parenchymatous, and in G'obia consists 
of a somewhat loosely compacted series of cell-rows 
running outwards. In Dictyosiphon, irregular branch- 
ing is fairly copious, in Gobia there is sometimes no 
branching at all, and if present it is always spare 
and irregular. Seytothamnus, about the development 
of which comparatively little is known, is repeatedly 
branched. Hairs are produced abundantly from the 
cortical cells, especially on young plants. 
The Reproductive Organs are represented, so far as 
is known, only by unilocular sporangia, which arise 
as the equivalents of cortical cells. The observations 
of Areschoug suggest that the zoospores produced in 
these may occasionally, at least, play the part of 
gametes, but the matter requires confirmation. So 
far as our knowledge of the group goes, it is plain 
