ALGAL UTILIZATION 449 



thickening agent in ice-creams, sherbets and pastries. It is also used 

 as a clarifying agent in brewing and wine-making. Carragheen has 

 a culinary use in the preparation of blanc-manges but it is also used 

 medicinally as a cough tincture and pharmaceutical emulsifier. 



For many years seaweeds have been employed on coastal farms 

 not only as a manure for the land but also as a stock food. Sheep and 

 catde will often eat seaweed and on one of the Orkney Islands 

 there is a race of sheep that feeds exclusively on seaweed. In Europe 

 several factories have been built to manufacture stock feed, in 

 nearly all cases the brown rock-weeds {Fucus, Ascophyllum) being 

 used though Laminaria may also be utilized. So far as value is 

 concerned the algal meal is as good as other stock feeds such as hay, 

 oats and potato tops, but this does not mean that they are as digest- 

 ible. Generally speaidng, it would seem that laminarin is the most 

 digestible material and therefore the time of harvesting is of im- 

 portance, i.e. harvesting at the period of maximum laminarin con- 

 tent. In the past this has not always been done and under such 

 circumstances the feed has not always been fully digested. 



The oarweeds and rock-weeds are also used as a manure on the 

 land. If there was not so much wet weight and the moisture was not 

 expensive to remove, it is probable that the algae would have a 

 wider use in this connexion. The seaweed can either be dug in 

 fresh (this seems best), allowed to rot on the surface, or else com- 

 posted with other organic material. Manurially the algae used have 

 a good nitrogen and potash content but they are low in phosphorus. 

 The nitrogen is not, however, freely available and takes time to pass 

 into the soil: seaweed manure is therefore of the slow but long act- 

 ing type. The amount of common salt present is not excessive as 

 one might have expected it to be. Naturally the composition of the 

 different species varies and also of the different organs, the leafy 

 parts usually being richer than the stipes. Seaweed manure is par- 

 ticularly valuable because of the trace elements that it contains and 

 the importance of these to good plant growth. One aspect that ap- 

 pears to have been neglected is the effect of these algae on the 

 physical properties of the soil. In view of the possible use of algin 

 (cf. p. 447) for this purpose it is clearly important that some study 

 should be made of this aspect. 



In China, Japan and Hawaii, seaweeds have been used for a long 

 time as human food. EarUer they have also been used in Europe, 

 but their use there has now died out. The young stipes of Lamin- 



