237 



genus, DermatolUhon, characterised by having a single apical pore in the hemisphe- 

 rical-conical conceptacles, sporangia "with short foot rising from the almost plain 

 disc" and developing, according to Rosanoff, between club-shaped (?) paraphyses. 

 In 1904 (Algol. Not. I. p. 3) however, he comes to the conclusion that these charac- 

 ters had not proved sufficiently constant, and did not form any distinct limit as 

 against the genus Liihophylliim. He therefore no longer maintains DermatolUhon 

 as a genus, but regards it as a sub-genus under the last-named genus, to which 

 Heydrich had already previously (Corallinacese etc., Ber. deut. hot. Ges. 15, 1897, p. 47) 

 reckoned Melobesia Corallince Crouan, and points out that it is further distinguished 

 by its anatomical structure, the hypothallium being formed by a single layer of 

 inclined cells. In 1909, (Algol. Not. VI, p. 57) however, it is again reinstated as a 

 genus, FosLiE now attaching greater importance to the mentioned anatomical char- 

 acter, and it was adopted by Svedelius in 1911. M. B. Nichols, who has subjected 

 some species of this relationship to closer investigation, (Univ. of California Publ. 

 in Botany vol. 3, No. 6, 1909) discusses some of the other characters cited by Foslie, 

 viz : the presence of a "plug" in the orifice of the sporangial conceptacles united at 

 the basis by a parenchymatic tap ; the position of the sporangia at the bottom of 

 the conceptacle, which in Melobesia is said to be almost flat, in Lithophyllum over- 

 arched; and the presence of a stalk cell under each sporangium in Melobesia. He 

 adopts the standpoint which Foslie then adhered to; i. e. not maintaining Dermato- 

 lUhon as a genus, but referring the species concerned to Lithophyllum, (L. macro- 

 carpum, pustulalum, tamidulum). He points out, however, that in so doing, "the 

 characters which separate Lithophyllum and Melobesia are not sufficiently well marked 

 to warrant two separate genera" (p. 361). With regard to the structure of the con- 

 ceptacles and the organs of reproduction, there is doubtless great similarity between 

 the two genera; at any rate, no thoroughgoing differences appear to have been de- 

 monstrated up to now. The vegetative structure seems to me to present an ex- 

 cellent distinctive character, as in Melobesia, we never find transverse pits between 

 the upright cell-series proceeding from the basal layer, whereas such are present 

 in all Lithophyllum species, including the subgenus DermatolUhon. On the other 

 hand, transverse fusions are of common occurrence in the Melobesia species, but 

 are wanting in Lithophyllum. This seems, as a matter of fact, to be the best 

 distinctive character between the two mentioned genera. 



As to how far there may be reason to make further exclusions from the genus 

 Melobesia, this must be left to further investigations to decide. Foslie, in 1900, 

 (Rev. Surv. p. 21) established a subgenus Heteroderma, which he characterises as 

 having the "thallus composed of more layers of cells" in contrast to Eumelobesia, 

 which should have but one layer, except as regards the frond near the conceptacles. 

 In 1905 however, (Remarks p. 102) a dilferent limitation is made, and in 1909, (Alg. 

 notes VI, p. 56) Heteroderma is raised to the rank of a genus, distinguislied from 

 Melobesia solely by the lack of hair-cells. I do not consider that we are justified 

 in dislinguish.iiig between two genera merely by the presence or absence of hair- 



