700 SUMMAKY OF CUERENT RESEAECHES RELATING TO 



data are advanced in support of this view. The nature of the stimulus 

 causing vernal reproduction is probably an intensification of those con- 

 ditions, which are liable to change in spring. Such intensification may 

 exceptionally take place at other times of the year, and lead to repro- 

 duction at other times than in spring. 



As regards the points of systematic interest, the authors confirm the 

 view that S. ternata Ripart is only a form of 8. neghcta, which they find 

 is a very variable species. They figure and describe another form which 

 ■appears to be new. In 8. varians, which has been described by G. S. 

 West as exhibiting frequently lateral conjugation, they have noticed 

 only scalaiiform conjugation, though they have often found the species 

 in the reproductive condition. On one occasion they found it doubled 

 back and conjugating with itself. S. affinis is figured with both scalari- 

 form and lateral conjugation in the same filament ; and other figures 

 show the two types of conjugation in 8. longata. 



Fresh-water Algae of the Great African Lakes.* — G. S. West 

 publishes a lengthy and detailed report upon the fresh-water algfe, 

 including phytoplankton of the third Tanganyika Expedition conducted 

 by W. A. Cunnington (1904-5). The collections were of an exten- 

 sive nature, and consisted largely of plankton obtained from the 

 three great lakes, Nyasa, Victoria Nyanza, and Tanganyika. The plank- 

 ton of Tanganyika is of special interest as being the first received from 

 that lake, and as containing species of a very noteworthy character. 

 The paper contains ;^)6 species and one genus of fresh-water alg£e, and 

 two Peridiniese, all new to science. The author devotes a chapter to the 

 special character of the phytoplankton, and gives a table showing the 

 distribution in the three lakes, and in a second table contrasts the rela- 

 tive frequency of the various species between July 1904 and February 

 1905. A systematic account of the algae of the collection is followed 

 by a general summary of the investigation. The algal flora of Tangan- 

 yika differs very much from that of Nyasa or Victoria Nyanza, but its 

 peculiarities are all of them such as could be accounted for by the 

 prolonged isolation of the lake. Those algaj of Tanganyika which 

 exhibit marine affinities may have been produced by a gradual increase 

 in the salinity of the water over an extended period of time. The 

 relatively small proportion of Chlorophycese in the plankton, and the 

 large proportion of Bacillarieas and Myxophycese, are also indications 

 that the water of the lake was at one time much more saline than it is 

 at present. In large bodies of fresh water, such as these central African 

 lakes, it would appear that a single sample of plankton obtained in a 

 ;stated locality must not be regarded as representative of the plankton 

 ■of the entire lake. 



Some British PhaBophycese.f — A. D. Cotton records three species 

 new to Britain, and makes notes on several other interesting members 

 •of PhfBophycege. The new records are Ascocydus affinis Sved., which 

 has never been found since it was first described ; Hecatonema diffusum 

 Kylin and 8trehlonema effiisum Kylin. The first of these was found on 



* Journ. Linn. Soc, xxxviii. (1907) pp. 81-197 (9 pis.). 

 t Journ. of Bot., xlv. (1907) pp. 368-73. 



