81 



immediately assimilate them. This view seems to explain the 

 remarkable difference in the composition of weeds growing so 

 close to one another. 



In many parts of the British Isles and France seaweed is 

 looked upon as a valuable general manure. Its value in this 

 respect is well brought out by analysis and depends upon the 

 fact that it contains about the same amount of nitrogen, much 

 less phosphate but more potash than rotted dung. As all 

 the nitrogen in seaweed is more or less albuminoid in character, 

 it has no manurial value till the seaweed has been allowed to 

 decay. It decays rapidly, however, and therefore quickly 

 becomes of value as a fertiliser. The potash of the seaweed is, 

 however, immediately available, for when seaweed is simply 

 washed in water a large amount of its potassium salts is leached 

 out. Again, all the potassium is present in seaweed in a soluble 

 form, either as sulphate or chloride, and therefore water need 

 only act on seaweed to make all its potash available. The case of 

 the phosphate is very similar to that of the nitrogen, as it does 

 not come into play as a fertiliser till the seaweed has been 

 allowed to decay. Seaweed is therefore a potash manure, and 

 may be used for crops especially requiring potash, such as 

 potatoes. Professor Hendrick has experimentally proved (op. cit.) 

 that " weight for weight seaweed gives just as great a crop 

 of potatoes as farmyard manure — but to get the best results 

 it should be supplemented with phosphate." 



The analyses show that about 15 to 20 per cent, of the 

 original seaweed is dry matter, and of this GO to 70 per cent, is 

 organic or combustible matter. When seaweed, therefore, is 

 used as a manure, only 3 per cent, of the 60-70 per cent, of the 

 organic matter is used, the remainder being practically valueless. 

 Hence at present (and in those places only, where seaweed is 

 used as a manure), only 15 per cent, (this being a maximum) of 

 the dry matter of seaweed has any commercial value. With 

 these facts in view the organic portion of seaweed has been 

 carefully analysed and subjected to very varied and different 

 processes. The resulting substances, though small in bulk and 

 in many cases obtained in a very impure state, seem to point to 

 the fact that seaweed (more especially of the fleshy type, such as 

 Laminaria digitata), when properly treated is capable of yielding 



