First, the macrophyte inventory of the river Danube in the strict sense is presented in 8 articles which occupy 100 of the total 229 pages of the publication. Then there are 6 additional articles comprising 106 pages that deal directly or indirectly with tributary rivers as well as channels situated in the Danube floodplains. The volume is enhanced by an introductory overview and a presentation of the parameters and methods used here: Trophic Index of Macrophytes (TIM); Mean Mass Index (MMO, MMT); Relative Area Length, Relative Plant Mass (RPM); sampled abiotic parameters and growth forms.

It is, however, striking that in an international study concerning a river that runs through as many as 10 countries, 8 articles in 14 are written by the authors Kohler or Janauer (in some cases as co-authors).

Since nowadays there are only a few comparably detailed presentations of the vegetation of running waters situated in a single river catchment, this macrophyte inventory of the river Danube has to be very much appreciated. Even though only a short section (4 \%) of the total length of the river of about 2,850 km is mentioned in the articles, the intention of this project remains exemplary.

Where the river Danube is concerned, the term "pilot study" has to be taken literally. In Germany, these sections are situated near Höchstädt (river-km 2538.0-2530.8), in Austria near Abwinden-Asten (river-km 2136-2119.5), in Slovakia in the region around the Gabcikovo hydropower station, in Hungary in the areas of river-km 1845-1828 as well as 1498-1468, in Yugoslavia near Novi Sad (river-km 1255-1260) and in Romania in the delta area.

The problems arising during the registration of the vegetation of running waters are well-known. While a qualitative registration depends, above all, on identification of the different species and is extremely time-consuming, there are several methods of differentiated ated registration concerning abundance and distribution. For the project described in this volume, a registration method was applied that uses a PME-scale of five levels which was initially published by KOHLER et al. (1971) and in this case was based on different survey units each having an equal length of 1,000 m. Certainly, different opinions may exist concerning the accuracy of the applied method. However, in this case, I would like to point out that it is precisely the use of only one specific registration and evaluation method of the vegetation of such a wide fluvial system that makes the study so interesting.

The presentation of the aquatic vegetation is divided into tables and figures concerning quality as well as distribution and abundance within the investigated sections on the right and left banks of the river, considered separately. This guarantees a good first overview that can reveal possible differentiations, disturbances or new substituting plant associations. This approach is not used consistently. In some articles it is totally lacking although the corresponding data might exist, since a number of indices quoted in those articles are even derived from those data.

Five articles deal with rivers that can more or less be regarded as tributaries to the Danube. Taking as an example the river Moosach, which has already often been described by Kohler and co-authors in former publications, one article explains the macrophytes and their characteristics as biological indicator species. Another article deals with the river Vils (Oberpfalz, Bavaria) which flows directly into the Danube. The long-term study of the running waters in the Friedberger Au near Augsburg, which has been carried out since 1972 and might surely be considered to be unique, is also amended by new data. The headwater of the Ipel' River (Slovakia), presented in another article, shows the special spe- cies inventory of a faraway headwater, since it is situated about 200 km away from its mouth into the river Danube. The river Izica, which crosses a karst region in Slovakia and is a tributary stream to the river Save, represents the most exposed example of a tributary river of the Danube. Finally, the presentation is completed by the investigations of hydrophytes in three partially saline channels situated in the Hungarian lower Danube valley.

The concluding article "Overviews and final remarks", written by Janauer, gives a short and good presentation of the species composition and explains special results. It represents a valuable overview of the pilot study which was carried out in 1998-1999. Finally, it becomes obvious that, excluding filamentous green algae, 40 species of hydro- phytes and amphiphytes as well as 9 bryophytes can be observed in the main stream of the Danube. Additionally, there are 22 hydrophytes and amphiphytes as well as 9 bryophytes and 4 taxa of Characeae which can be found in the Danube oxbows and flood plain channels. The species composition reported here does not reveal any surprising results concerning the presence of special species. The (according to the authors) unexpected presence of Lemnaceae (p. 227) is not unusual since pleustophytes are not all that rare in the potamal areas near the banks of large, polymorphic streams; smaller standing waters can often develop in these regions owing to backflowing waters, and in sheltered reed bank areas. Taking as an example the development of Elodea nuttallii, the authors give a brief description of the problems arising from the existence of neophytes in other riverine waters. Besides Elodea canadensis, which is also relatively common throughout the investigation area, and Vallisneria spiralis, which is present in the Danube Delta, the Hungarian part of the river Danube is characterised by Cabomba caroliniana, which here accounts for 10 \% of the total phytomass.

It is quite annoying that, in some cases, the descriptions are not precise; for example, a table that is said to represent common algal species whereas in fact only the Characeae are meant, or a map of the river Ipel indicating the wrong flow directions.

The volume was not intended to be a monographic approach, as might have been expected from its title. However, the content is interesting for every botanist working in the field of running waters, even though the price of the volume is high.

Phytocoenologia 35 (2-3) 8/2005