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, it is interesting 

 to note Kjellman's observation of the normal growth 

 and fructification of Algae during the dark arctic 

 night and at a mean temperature of 1C. Obser- 

 vations of any notably high temperatures resisted in 

 the sea arc of course of small physiological interest 

 compared with the temperatures resisted by fresh- 

 water Algae 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 2 . A sudden change of water is also mis- 

 chievous ; and added water (whether fresh- water to 



