8 SEAWEEDS 
floras than of land floras, and when its operation is 
tested by a survey of the pelagic vegetation, this 
view is much enforced by the result. Pelagic free 
floating Algae removed from the influence of coast 
and river waters, rise and fall of tides, nature 
of bottom, &c., and left to the nearly exclusive 
operation of temperature in stamping their char- 
acter, are found to respond to this influence and to 
vary with areas of temperature in the sea. As an 
extreme term in resistance to adverse conditions of 
temperature and supply of light, ib is interesting 
to note Kjellman’s observation of the normal growth 
and fructification of Algs during the dark arctic 
night and ata mean temperature of—1°C. Obser- 
vations of any notably high temperatures resisted in 
the sea are of course of small physiological interest 
compared with the temperatures resisted by fresh- 
water Algw inhabiting hot springs. 
In the culture of seaweeds in aquaria it has been 
found that forms from deep water are peculiarly 
susceptible to rise of temperature and undue illumin- 
ation, so much so that merely for their transport it 
is necessary to choose a cloudy day, especially if in 
summer, and the use of ice is almost always advis- 
able. A cool chamber from which direct sunlight is 
excluded is a condition of success in the culture of 
most seaweeds. One way in which these plants may 
be killed by too much care is in the attention paid to 
aeration of the water. Very little is necessary, since 
the air so introduced has been found to carry off too 
much CO,. A sudden change of water is also mis- 
chievous; and added water (whether fresh-water to 
