DISTEIBUTION OF MAEINE ALG.3E. 171 



the like, many tons of coal per annum to most of our 

 great ocean-going lines. Let us take the case of a 

 steamer making the voyage from this country to the Cape 

 and back, if she has received no overhauling in the mean- 

 time, her bottom will be so overgrown with seaweed on 

 her second return trip, that it will need many extra tons 

 of coal to drive her, especially if a record-breaking speed 

 is demanded. (I may mention casually that this difficulty 

 attends only iron and steel vessels — the old wooden 

 copper-bottomed boats were protected by the exfoliating 

 of the copper.) Now in such a case, I mean a voyage to 

 the Cape and back, through many swiftly changing tem- 

 peratures, the result is exactly as might be expected. 

 Cosmopolitan forms — it is only right to say that these 

 predominate in all cases — like Enteromorplia — are by far 

 the most frequent ; they practically exclude the others. 

 Let us take on the other hand the case of one of Her 

 Majesty's ships which has returned during the summer 

 months from service in the Mediterranean, or a ship that 

 has been lying in a foreign port not far distant. She has 

 a varied marine flora arranged in green, red and olive and 

 brown zones on her sides and bottom. In a few days' 

 steaming she is in another natural region. The changes 

 of temperature, etc., are doubtless fatal to the great 

 majority so far as a chance of acclimatization is concerned. 

 Are they so to all? I do not believe it. It would weary 

 you to give here the details observed under this head, but 

 I cannot refrain from mentioning one remarkable case. 

 Mr. Batters has found at Berwick-on-Tweed an Australian 

 seaweed, in all probility detached from a passing vessel. 

 It is hardly likely that such migrations have occurred 

 often, and they are not in contemplation, but rather such 

 movements from one similar region to another as the 

 Atlantic passage from this country to the United States, 



