52 THE PLANT. 



water in which the plant had grown contained only 4 

 parts of potash to 10 parts of chloride of sodium. In the 

 plant the relative proportion of the sulphuiic acid to the 

 phosphoric acid was 10 to 14 ; in the water, 10 to 3. 



It is quite the same with marine plants. Sea-water 

 contains for 25 or 26 parts of chloride of sodium 1-21 to 

 1-35 of chloride of potassium ; but the plants growing in 

 it contain more potash than soda. The kelp of the 

 Orkney Islands, which consists of the ashes of many 

 species of fucus,* contains for 26 per cent, of chloride of 

 potassium only 19 per cent, of chloride of sodium. 



Sea-water contams manganese, but in such exceedingly 

 small quantity that it would certainly have escaped 

 analysis, were it not invariably found among the ash- 

 constituents of many marine plants. The ash of Paclina 

 pavonia (a species of tang) is found to contain of this 

 mineral even more than 8 per cent, of the weight of the 

 dried plant, f 



By the same power of selection the laminaria withdraw 

 from the sea-water in which they grow the iodine com- 

 pounds present in it in such exceedingly minute quanti- 

 ties. Chloride of potassium and chloride of sodium have 

 the same form of crystalhsation, and so many other 

 properties in common, that without the aid of chemical 

 means we cannot accurately distinguish the one from the 

 other. But the plant clearly discriminates between the 



* See Godeclien's analysis of the ash of different species of fucus. 

 (' Annal. d. Chem. und Pharm.' liv. 351.) 



I To give some idea of the extraordinary power which this plant 

 must possess to withdraw the manganese from sea-water, I need 

 simply state that the quantity of this metal in sea-water is so exceed- 

 ingly small, that I coiild find distinct traces of it only by subjecting 

 the sesquioxide of iron, obtained from twenty pounds of sea-water, 

 to a most searching analysis, (Forchhammer and Poggendoff, xcv. 

 p. 84.) 



