306 THE ALGAE 



and also constructed of the wide and narrow tubes. The thallus is 

 surrounded by a cuticular layer that exhibits a pseudo-cellular 

 pattern, and which includes within the cuticle and among the peri- 

 pheral tubes firm- walled spores of various sizes; in N. pseudo- 

 vasculosa the spores were definitely cuticularized and so the sug- 

 gestion was made that these were land plants or parts of a land 

 plant. The side tubes, which have thin pale brown walls, are trans- 

 lucent in appearance and exhibit distinct characteristic annular 

 thickenings. The cuticle, which is apparently readily detached, 

 possesses distinct cell outUnes that were probably made by the ends 

 of the wide tubes from the ordinary tissue where they became fused 

 together at the periphery, as in the living genera Udotea and Hali- 

 meda. Another species Nematothallus radiata is more imperfecdy 

 known. 



From the structure described above it can be seen that the mem- 

 bers of this group are strongly reminiscent of the Laminariales and 

 Fucales, and it is tempting to suppose that they represent land 

 migrants from one of these groups. There is no evidence, however, 

 of any parenchymatous structure, so that if they were indeed mem- 

 bers of that group they would be aUied to forms with a multiaxial 

 type of construction. Problems that have to be solved are: (i) The 

 cuticularized spores; whilst no such spores with hard outer walls 

 are known from the brown algae they are recorded from the Chloro- 

 phyceae, e.g. Acetahularia. However, the suggestion that the spores 

 may have developed in tetrads adds a further compUcation, at any 

 rate so far as an algal ancestry is concerned, because the Dictyotales 

 and tetrasporic Rhodophyceae do not show the state of differentia- 

 tion found in these fossil plants. (2) The presence of a deciduous 

 cuticle. In this connexion one or two Laminariales are known to 

 shed cuticles during reproduction, and the present author has 

 found a deciduous cuticle on plants of Hormosira, a member of the 

 Fucales. It may be suggested that the plants perhaps had the ap- 

 pearance of a Lessonia or even of a Durvillea, and a stem diameter 

 of two to three feet does not preclude them from being algal in 

 character because several of the large Pacific forms may have stipes 

 of ahnost this size (cf. p. 183). It has also been suggested that these 

 forms are related to the Codiaceae, expecially Udotea, and in 

 certain respects it is true that they have the structure of a siphon- 

 aceous plant. Here again there are several problems that need to be 

 answered : (a) the presence of two sizes of tubes; (b) the presence of 



