FOSSIL FORMS 277 



gestion that the spores may have developed in tetrads adds a 

 further compUcation, at any rate so far as an algal ancestry is con- 

 cerned, because the Dictyotales and tetrasporic Rhodophyceae do 

 not show the state of differentiation found in these fossil plants. 

 (2) The presence of a deciduous cuticle. In this connexion one or 

 tv^o Laminariales are known to shed cuticles during reproduction, 

 and the present author has found a deciduous cuticle on some pre- 

 served plants of Hormosira, a member of the Fucales. It may be 

 suggested that the plants perhaps had the appearance 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 almost this size (cf. 

 p. 180). It has also been suggested that these forms are related to 

 the Codiaceae, especially Udotea, and in certain respects it is true 

 that they have the structure of a siphonaceous plant. Here again 

 there are several problems that need to be answered: {a) the 

 presence of two sizes of tubes ; {h) the presence of a cuticle ; (c) the 

 presence of cuticularized spores; {d) the large size of stem. 



The answer to the last problem has already been suggested (see 

 above) but cuticles in the Codiaceae have not been recorded, 

 although the present author has been able to detect a structure 

 something like a cuticle in Halimeda; nor have any species been 

 reported that possess two distinct sizes of tubes, although grada- 

 tions in size occur in both Udotea and Halimeda. In this connexion 

 it may be of interest to refer to Tilden's unsupported suggestion 

 that the land plants arose from forms such as C odium and C aider pa. 

 It must be admitted that there are no living members of the 

 Codiaceae with stems that approach anywhere near the size of 

 those of Nematophyton. This, however, is not an insuperable ob- 

 jection as the Nematophytales may bear the same relation to the 

 livmg Codiaceae that the fossil Lepidodendrons bear to the living 

 Lycopodiales. For the present, however, the problem must be left 

 in the hope that further evidence will accumulate. 



REFERENCES 



Spongiostromata. Black, M. (193 3)- Philos. Trans. B, 222, 165. 



Evolution. Delf, M. (1939)- ^^"^ Phytol. 38, 224. 



Evolution. Fritsch, F. E. (1935)- Structure and Reproduction of the 



Algae, vol. i, p. 12. Camb. Univ. Press. 

 Heterotrichy. Fritsch, F. E. (1939)- Bot. Notiser, p. 125. 



