178 SOME RECENT RESEARCHES IN PLANT PHYSIOLOGY 



on antagonism of ions, for he finds sea-water to be a 

 perfectly balanced solution in this respect. 



Quite similarly, the destructive action of fresh water upon 

 seaweeds is very noticeable. Yendo (1914) has recently 

 drawn attention more particularly to this aspect on account 

 of the serious losses to Japanese seaweed industry resulting 

 from it. 



Some algae, such as species of Enteromorpha, can with- 

 stand sudden alternations of fresh and salt water. These 

 are usually found, in the British Isles as well as in Japan, 

 growing on 'those portions of the beach which are bathed 

 in a stream of fresh water at low-tide, but by the sea 

 during high-tide. Others, normally growing in the open 

 sea, can accommodate themselves to a lesser salinity. 

 Yendo illustrates this by the behaviour of Fucus vesiculosus, 

 which may be found in a brackish lagoon and in the sea, 

 but not in the connecting channel, where fluctuations of 

 salinity occur. 



With a view to testing the nature of the equilibrium 

 between the osmotic pressure of a seaweed and the sur- 

 rounding salt water, the following experiment was carried 

 out by Dixon and Atkins : A quantity of Ascophyllum 

 nodosum was collected near Kingstown, Co. Dublin, and 

 was immediately brought to the laboratory and pressed. 

 It was not treated with liquid air, as at the time the 

 authors had not discovered the necessity for this. How- 

 ever, as the results show, the error introduced in this case 

 cannot have been of any considerable importance. A 

 portion was kept in darkness in sea-water for twenty- 

 four hours, and was then pressed; while a portion of the 

 same sample was placed in sea-water to which slightly 

 more than an equal volume of fresh water had been added, 

 for three and a half hours. Table XLV. shows the values 

 of A, P, and M (the mean molecular weight), so obtained. 



