176 Algae. 



Odontotropis, 1 Orthoneis, 4 Paralia, \ Peronia ?, 3 Plagiogramma, 4 

 Pleurosigma, 2 Podosira, 2 Pseitdoaulisciis, 1 Pseudoceratauliis, 1 Pseiido- 

 mastogloia, 1 Pyrgodiscus, 6 Pyxilla, 5 Rhabdonema, 1 Rhaphoneis, 

 1 Rhizosolenia, 5 Rhopalodia, 3 Rutilaria, 1 Scoliopleiira, 4 Stauroneis, 

 6 Staurosira, 1 Stephanodiscus, 3 Stephanopyxis, 6 Stictodiscus, 1 Stignio- 

 phora ?, 6 Stylobiblium, 18 Surirella, 1 Syndetoneis, 5 Synedra, 3 7"er/7- 

 sinoii, 2 Tetracyclus, 45 Triceratium, 11 Trinacria, 1 Vanheurckella und 

 3 Zygoceres. G. Gutwinski (Krakau). 



West, W. and G. S. West, Pres h water Algae fromthe 

 Orkneys and Shetlands. (Transactions and Proceedlngs 

 of the Botanical Society of Edinburgh. Vol. XXIII. Pt.'l. 

 1905. p. 3—41. 2 pls. 



The authors visited these Islands during August 1903 for the pur- 

 pose of studying the distribution of British freshwater algae. The pre- 

 sent paper enumerates the species collected which number 447 inchiding 

 5 new to science: Closterium exile, Euastrum montanum, Cosmarium 

 subcontractutn, Staurastrum affine and 5. boreale. There are also some 

 new varieties described. In the Orkneys, the only islands investi- 

 gated were the southern part of P o m o n a and the northern part of 

 Hoy. In the Shetlands, Bressay and the Mainland only were 

 visited. Comparisons are drawn between the freshwater algae of these 

 Islands and those recorded from Iceland and the Faeröes by Bör- 

 gesen. 1 18 Desmids are common to the Faeröes, Orkneys and Shet- 

 lands, and 50 species of Desmids out of 58 recorded from Iceland 

 are also found in these Islands. Among the phytoplankton were Genicu- 

 laria Spirotaenia de Bary, Closteriopsis longissima Lemm. var. tropicuin, 

 and Crucigenia irregularis Wille, the latter being also recorded from 

 Norway. Of the 52 species of Faeröese plankton, enumerated by 

 Börgesen and Ostenfeld, 28 occur in the plankton of the Shet- 

 lands. A comparative table is given of species of phytoplankton from 

 the Orkneys, Shetlands and Faeröes. The general systematic 

 account of the coUections contains some interesting notes. Novelties 

 and Interesting forms are figured on two plates. 



E. S. Gepp-Barton. 



Williams, J. Lloyd, Studies in the Dictyotaceae. III. The 

 periodicty of the sexual cells in Didyota dlchotoma. 

 (Annais of Botany XIX. No. XXVI. Oct. 1905. p. 531 — 

 5bO. 5 diagrams in text.) 



During the course of his cytological investigations on Dlc- 

 tyota dlchotoma, the author has made a careful study of the 

 periodicity of the sexual cells of that species. He finds that each 

 crop is initiated, matured, and discharged all within a fortnight, 

 and that a general liberation of the oospheres and antherozoids 

 of the locality takes place on a certain day, or sometimes two 

 or three days, immediately after the highest spring tide. Although 

 this may be regarded as a general rule, there are of course 

 variations and exceptions, of which the author has made a 

 systematic study since 1897 to the present time. The interesting 

 results of these studies are embodied in the present paper. 



A general description of the sexual plant is first given. 

 The germling begins to elongate in May, and though repro- 

 duction may occur in June it is not common tili the end of 

 July; it is continued throughout August and September, after 



