Palaeontologic. — Algae. 167 



On the whole the characters observed in M. rnnUirame accen- 

 tuate the relation of the genus Mesoxyloii to Cordaites. 



Agnes Arber (Cambridge). 



Koldepup Rosen vinge, L., The Marine Algae of Den mark. 

 Contributions to their Natural History. Part II. Rhodo- 

 phyceae II. [Cryptonemiales). (K. Dankbke Vidensk. Selsk. Skrifter. 

 7. "R. VIT. 2. 132 pp. 2 pl. 128 text figs. Köbenhavn 1917 (issued 

 1918).) 



40 species are mentioned, belonging to the foUowing families: 

 Ditniontiaceae, Nemastornataceae , Rhisophyllidaceae , Squamariaceae, 

 HUdenhrandiaceae, Corallinaceae and Gloiosiphoniaceae. Of almost 

 all the species the structure of the frond and the structure and 

 partly the development of the organs of reproduction are described 

 and tigured, further the occurrence of the species in the Danish 

 waters 



Two new species of Squamariaceae are described: Criioriopsis 

 danica and Cruoriella codana. The sexual organs and the cystocarps 

 which are little known in this family are described in four species 

 iPetrocelis Hetinedyi, Critoria pellita, Cruoriella codana and Cr. Dybyi). 

 . The family Hildenbrandiaceae which in later time has been 

 abandoned is here restored as a particular family intermediary 

 between the Squamariaceae and the Corallinaceae, characterized by 

 the want of incrustation with lime of the frond , by the presence 

 of immersed'conceptacles of sporangia and by oblique divisions of 

 the sporangia. Sex organs are unknown. The development of the 

 conceptacles is described in Hildenbrandia. The transversal outline 

 of the conceptacles increases by the continued production of spo- 

 rangia, new vertical filaments being engaged in and partly consumed 

 by this production. The upper parts of these filaments, forming 

 the roof, finally decay. 



Corallinaceae. The cells of the filaments of which the frond is 

 coraposed are always connected b)' pits (pores) in the transversal 

 walls. In the genus Lithophyllum , the cells are also connected with 

 the cells of other filaments by transverse pores in the vertical 

 walls. These pores probably arise in a similar manner to the se- 

 condar37' pores in the Rhodomelaceae , though the Cooperation ofthe 

 nuclei has not been demonstrated. In all the other genera such 

 pores are wanting. but in these plants the cells possess another 

 means of entering in connection with cells in other filaments, viz. 

 b}' forming open Communications between them, the separating 

 wall being partially dissolved, as first described by Rosanoff. 

 The author has found that these fusions, which frequently take 

 place between more than two cells, may be foUowed by fusion of 

 the nuclei. Hyaline hairs frequentlj' occur in the genera Melohesia, 

 Lithophyllum and Corallina. The cells producing them have been 

 described by Rosanoff as heterocysts, the author proposes to 

 name them trichocytes. 



The sporangia are divided by one transversal or by three pa- 

 rallel walls into two or four spore-cclls. In the latter case the 

 divisions are frequently almost simultaneous, and, at least in Co- 

 rallina officinalis, the division of the nucleus into four takes place 

 long before the celldivision. The number of spores in the sporan- 

 gia is constant in most of the species, either 4 or 2, but in some 

 species both tetrasporic and disporic sporangia are met with; the 



