president’s address. 
163 
20 metres in the Lake of Geneva, and yearly variations at 
a depth of 80, 100, or 120 metres. For comparison it may 
be added that in the Mediterranean Sea daily variations are 
felt to a depth of 18 metres, while annual variations occur 
down to a depth of 400 metres ; in the China Sea annual 
variations cease at a depth of 185 metres with a temperature 
of 15.6° C. 
The climate of lakes is far more rigorous than that of the 
sea, owing to the greater variations of temperature which 
occur in the smaller bodies of water. 
Of high temperatures a reading of 127. 5 0 C. has been 
recorded at the bottom of the Great Geyser in Iceland, 
but that of the surface is between 76° C. and 8q° C. 
I do not think any life higher than Algae and Bacteria has 
been found in water of a temperature greater than 6o° C. 
( - 140° F.), in which Crustacea and Insect Larvae have 
been known to occur. 
The organisms most tolerant of heat are the Bacteria, and 
among them the Bacillus Thermophilus prefers a temperature 
of between 63° and 70° C.( = i58° F.), but can exist up to 
72 0 C. It finds a temperature of 42 0 C. too cold for it. 
The amount of salts dissolved in the water, and the nature 
of such salts, has a great influence upon animal life, and 
perhaps even more upon plant life, and is a more important 
factor in distribution than climate. 
The nature of the substratum is of importance only in the 
smaller expanses of water, and then chiefly affects those 
plants which root upon the bottom. 
Of animals the majority of families belong exclusively 
either to salt water or to fresh ; but there are distinctive 
brackish water forms, and there are also quite a number of 
most interesting species which inhabit on the one hand fresh 
water, while their close allies are marine, or on the other 
hand, inhabit the sea, while their close allies are limnetic. 
