676 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Phymatolifhon Fosl. (3 sp.), ClathromorpJmm Fosl. (4 sp.), Lithothamnion 

 Phil, emend. (64 sp.), Chsetoliihon Fosl. (1 sp.), Goniolithon Fosl. (13 

 sp.), Lithophyllum Phil, emend. (44 sp.), Melobesia Lamour emend. 

 (11 sp.), Dermatolithon Fosl. (5 sp.), Choreonema Schm. (1 sp.). 



Ulva latissima and its relation to the Pollution of Sea-Water.* — 

 From observations made on the growth of this sea-weed in Belfast 

 Lough, where it is extremely abundant, and on cultures, Prof. Letts and 

 J. Hawthorne conclude that the sewage-like stench is largely due to 

 the sulphuretted hydrogen given off by its fermentation. The decaying 

 sea-weed appears to be attacked by two micro-organisms in succession ; 

 the first is a spore-forming bacillus, the product of fermentation con- 

 sisting mainly of propionic acid derived from the decomposition of the 

 albuminoids ; the second producing ultimately sulphuretted hydrogen 

 from the reduction of sulphates. The Ulva flourishes in polluted water, 

 and is generally, when present in large quantities, a sign of the presence 

 of sewage. By its capacity of producing sulphuretted hydrogen, it 

 enormously increases the evil. It has a remarkable power of absorbing 

 nitrogen from polluted sea-water in the form both of ammonia and of 

 nitrates. 



Dictyosiphon.f — Dr. S. Murbeck gives an account of this genus of 

 Phaeosporese. The growth of the " hairs " is fully described and figured ; 

 also the formation of pits, and the consequent enlargement of the sur- 

 face of the thallus. The occurrence of " hyphae " in the thallus is 

 noted in the case of D. foeniculaceus. This species is epiphytic on 

 Chordaria, the two plants showing a close intermingling at the point of 

 junction. 



Classification of Desmidiaceae.J — Prof. C. E. Bessey proposes the 

 arrangement of the American genera of desmids under three tribes, viz. 

 the Desmidieae, Arthrodiea?, and Cosinarieae. The Desmidieae are charac- 

 terised by having the cells in unbranched filaments, and comprise the 

 genera Gonatozygon, Genicularia, Gymnozygon, Phymatodocis, Hyalotheca, 

 Desmidium, Sphserozosma, and Onyclionema. In the Arthrodieae the cells 

 are solitary and elongated, and not at all, or but moderately, constricted ; 

 the genera are Entospira, Mcsotsenium, Penium, Arthrodia (Closterium 

 Nitzsch), Tetmemorus, Docidium, and Pleurotsenium. In the Cosmarieaa 

 the cells are solitary, broad, and deeply constricted ; they include the 

 genera Cosmarium, Pleurotseniopsis, Cosmocladium, Arthrodesmus, Euas- 

 trum, Micrasterias, Xanthidium, and Staurastrum. 



Structure of Diatoms. § — F. Keeley states that, in a certain group 

 of species of Aulacodiscus — A. oreganus, Rogersii, Janischii, &c. — we 

 have a structure differing essentially from that of other diatoms. The 

 typical honeycomb cellular structure is marked by the unusual character 

 of the external plate, which differs from that of other diatoms in having 

 the finer secondary structure between, rather than over, the large cells 

 of the middle plate. A. oreganus is one of the few diatoms that show 

 bright colours with central transmitted light. 



* Proc. Roy. Soc. Edinburgh, xxiii. (1901) pp. 268-94 (3 pis.). 

 t Vidensk. Skrift, Matheni.-naturv. Klasse, No. 7. 1900. See Journ. Bot., xxxix. 

 (1901) p. 251. X Trans. American Micros. Soc, xxii. (1901) pp. 89-96 (1 pi.). 

 § Proc. Acad. Nat. Sci. Philadelphia, 1901, pp. 321-3. 



