98 SEAWEEDS 



DICTYOSIPHONACE.E. 



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 

 Didyosiphon is parenchymatous, and in Gobia 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. Scytothamnw, 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 



