ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 339 



the plankton of the Schoenenbodensee. He gives a table of the relative 

 abundance or absence of the species month by month, and analyses the 

 results. In another table he shows the presence or absence of 1(K> of the 

 commoner algae in Schoenenbodensee and four other small Swiss lakes. 

 Schoenenbodensee is relatively rich in Chlorophycefe, Desmidiaceae, and 

 Diatomaceaj, and poor in Scbizophyta, PeridineaB, and Flagellatse. 

 Therein it differs from the small lakes of the Swiss plateau. In fact the 

 more elevated the lake, the less do its characters depend on its depth, 

 and the more is the composition of its microflora influenced by variations 

 in its temperature. 



Plankton Studies in Salzkammergut.* — K. von Keissler gives 

 lists of the phytoplankton collected in seven lakes in Salzkammergut, 

 at a height not exceeding 1000 m. above sea-level. Several rare species 

 were found. A comparison of the respective floras shows that neigh- 

 bouring lakes, when examined at the same time of year, may exhibit a 

 totally different plankton. Again, some of the lakes had much and 

 some but little plankton, and in cases where two neighbouring lakes 

 showed plentiful material, the composition of each was different. Among 

 the records is a species of Melosira, a genus which has till now only been 

 recorded from a few Austrian alpine lakes. 



Marine Plankton.! — A. Nathansohn writes an important paper on 

 the influence of vertical movements of the water on the production 

 of marine plankton. He criticises the work of Brandt and his ex- 

 planation of the fact that the amount of plankton is much greater 

 on the edge of cold regions than in warm currents. Brandt considers 

 that this is connected with the compounds of nitrogen, which, accord- 

 ing to his theory, are found more plentifully in colder than in warmer 

 waters, because denitrifying bacteria break up the nitrates and nitrites 

 present more easily in warmer water. Nathansohn holds that Brandt's 

 theory does not account for all the facts, and that though denitrifying 

 bacteria are certainly widely distributed in the sea, their power of 

 separating free nitrogen from nitrates is merely a facultative one, 

 since in the open sea neither nitrites nor nitrates are formed from 

 nitrifying bacteria. On the other hand, he regards as a very im- 

 portant factor the vertical currents in the sea, which arise from many 

 causes. A large number of dead organisms sink from the top to the 

 bottom layers of water, thereby removing a considerable quantity of 

 important nutritive material from the upper layers, and this has to be 

 returned by upward currents to the surface. In shallow waters this 

 depletion cannot take place, which explains the relative richness of these 

 regions. An investigation and comparison of various regions has 

 allowed the author to deduce the following general rule, namely, that 

 the regions rich in plankton in the far north and south, and, to a 

 certain extent, the tropical seas, are distinguished by currents ascending 

 vertically upwards ; whereas in the temperate regions, poor in plankton, 

 there are either no vertical currents, or they are descending ones. In 

 the last chapter the various nutritive matters are described, of which 



* Oesterr. Bot. Zeitschr., Ivii. (1907) pp. 51-8. 



+ Abh. Math.-Phys. k. Sachs. Ges. Wiss., xix. (1906) No. 5; Bot. Zeit., Ixiv. 

 (1906) pp. 345-8. 



