428 
Algae. 
demonstrated during the investigation of material collected by the 
“National” expedition, that the plankton of colder seas is more 
abundant than in warmer seas. The tropical seas have a higher 
temperature and more intense illumination, yet in spite of the grea- 
ter variety in species and more striking forms of the organisms 
there, it is no doubt the case that life is at least as abundant, 
sometimes much more abundant, in polar and temperate seas. The 
highly productive fisheries of arctic and temperate seas in high 
latitudes suggest a larger food-supply and the quantitative observa- 
tions :of the Kiel planktologists confirm this. “The cause can only 
be that some indispensable foodstuff of the plants is more abundant 
in the colder seas than in the warmer ones”. The “producers of 
the sea” are taken to be diatoms, peridinians, and some flagellate 
protozoa. The indispensable foodstuff is that one which is present 
in minimum quantity, relatively. The inquiry is pursued as regards 
nitrogen compounds, silicic acid, and phosphoric acid, the three 
groups of substances which seem to be present in small quantities 
in the sea, and are yet essential for the organisms just mentioned. 
As regards nitrogen, Raben’s results show that the average amount 
of nitrogenous compounds in Baltic and North Sea water is 
about 0*2 parts in one million; there is also a seasonal fluctuation, 
the minimum being in August the hottest month of the year. Phos¬ 
phoric acid has been found to be more abundant in warmer seas 
than in colder ones, and in the North Sea it occurs in lar- 
gest quantity in autumn. Silicic acid, according to Raben, varies 
from a maximum (P4 parts per million) in February (in 1903) 
to a minimum (0*65) in May, with a secondary maximum (IT) in 
November. The abundance of diatom-plankton in Kiel Bay, if 
expressed in a curve, shows a principal maximum in April, and 
a secondary maximum in October. Correlating these, the author sug- 
gests an accumulation of silica in the sea during winter, and in 
spring with increased sunlight, there is an increased propagation 
of vegetable life; this foodstuff is used up and a minimum of silica 
occurs in May, just after the diatoms have been most abundant; a 
slight increase in silica from May to August is accompanied by a 
second period of diatom abundance. Hence silica is one of the food- 
stuffs which is sometimes present in the sea in minimal proportion. 
The available data also suggest that in the warmer periods of the 
year when nitrogen compounds are least in quantity, it may be 
regarded as a foodstuff in minimal proportion. The action of deni- 
trifying bacteria in the sea has been demonstrated, and Baur’s 
observations indicate that the evolution of free nitrogen, which is 
little or nothing in cultures at 0° C., increases rapidly with increase 
of temperature. This is given as “a very probable explanation of 
the relative scarcity of nitrogen compounds in the warmer seas and 
the decrease in the amount of these in colder seas in the warmer 
months of the year.” W. G. Smith. 
Lakowitz, Die Algenflora der Danziger Bucht. Ein Bei¬ 
trag zur Kenntnis der Ostsee flora. Hgg. vom West- 
preussischen Bot.-Zool. Verein mit Unterstützung der 
Provinzial-Kommission zur Verwaltung der Westpreuss. 
Provinzial-Museen. (p. 1—141. Mit 70 Textfig., 5 Doppeltateln 
in Lichtdruck und einer Vegetationskarte. Danzig 1907. (Komm. 
Verlag W. Engelmann, Leipzig.) 
Verf. legt hier die Resultate zwanzigjährigen Sammelns und 
