4 8 
Pehr Olsson-Seffer. 
that often changes through a large amount of freshwater being 
brought down by the rivers, and then for some time floating on the 
surface of the usual sea water, which contains a greater percentage 
of salts and consequently is heavier. 
The rapidity with which a change in salinity takes place is 
further of the greatest importance for those plants which occur on 
the submerged beach. Many algas which, as a rule, are able to 
live in salt water of the most extreme degrees of salinity, cannot 
bear a rapid change in this amount of salt, because of the consider¬ 
able change in osmotic pressure which results in the cells. 
Temperature of sea water. This factor is of some importance 
for the distribution of sand strand plants. In northerly latitudes, 
especially in some parts of the Baltic, where the water is liable to 
be converted into ice during winter, the vegetation on the submerged 
beach is very scanty, the plants are low and of a poor stunted 
growth. 
The temperature of the sea water also to some extent influences 
the atmospheric temperature on the coastal sand formations. The 
writer’s observations of the temperature of the sea water have 
been confined to the Baltic and to the coast of South Queensland. 
In the Baltic, especially in the northern part, great variations 
in the temperature of the water occur. These changes are caused 
partly by the varying direction of the winds, or correspond to the 
seasons. During summer the surface water is often heated 
considerably, sometimes to 16° C. in the open sea, or 20-22° C. in 
sheltered inlets, while in winter ice formation takes place. Con¬ 
tinuous land winds often cause a fall of the temperature by driving 
seawards the warm surface water, which is then replaced by cold 
water. This is especially evident on steep, open shores. 
Solar radiation greatly affects the temperature of sea water. 
In sheltered bays its influence is greater than on the open sea. An 
observation by the author, described in another place, 1 showed that 
while the temperature of the sea water in a small inlet in the 
Finnish Archipelago was 20-6° C. in the early morning with an 
atmospheric temperature of 23° C. and a salinity of 0-521%, it had 
increased in six hours, during which time the solar radiation was 
intense, to 24" C. During the same period the atmospheric tem¬ 
perature had risen to 29° and the percentage of salt to 0-564. 
As a rule, the surface temperature of the water is higher than 
1 Nagra iakttagelser ofver hafsvattnets salthalt i Finska Skargiird- 
shafvet. Geogr. For. Tidskr., XI., p. 262, 1899. 
