448 THE ALGAE 



countries with coastlines explored their red algae in order to find 

 alternative sources. As a result, suitable agar was produced from 

 Gelidium cartilagineum on the Pacific coast of America and in South 

 Africa, from Gracilaria confervoides in Carolina, South Africa and 

 AustraUa, from Hypnea musciformis in Carolina, from Gelidium 

 pulchellum and G. latifolium in Ireland, from Chondrus crispus and 

 Gigartina stellata in England, from Suhria vittata in South Africa 

 and from Pterocladia lucida and P. capillacea in New Zealand. The 

 weed is usually hand picked from the rocks, e.g. England and New 

 Zealand, but in California it is collected by diving from boats. In 

 CaroHna the Gracilaria and Hypnea are collected by stop nets, but 

 in AustraHa the beds are in deeper water and a special trawl is used 

 for the collection of the plants. 



The gelatinous material that is extracted from these algae is com- 

 monly known as gelose. The agarophytes can be divided into three 

 groups on the basis of the setting power of the gel. 



(a) Gelidium type : decoction sets firm even if dilute. 



ih) Gracilaria^ Hypnea type : decoction sets firm if more con- 

 centrated or if electrolytes added. 



{c) Chondrus type : only sets firm if very concentrated. 



Japanese agar consists of the calcium or magnesium salt of a 

 sulphuric acid ester of a short chain of galactose residues. It is 

 Hkely that aUied compounds form the gelUng material in other 

 agarophytes, and this accounts for the variation in properties of the 

 different extracts. A special name is given to the extract from Irish 

 Moss or Chondrus^ which is called Carragheenin from the local 

 name of Carragheen for the alga. This substance is known to 

 differ chemically from agar though it is still an ethereal sulphate. 

 The Irish Moss industry is primarily developed in Ireland and 

 Massachusetts. The name is sometimes appHed to algae elsewhere, 

 e.g. New Zealand, but it does not then refer to Chondrus but usually 

 to a Gigartina, 



In some species there is a seasonal periodicity in the amount of 

 gelose the algae contain, e.g. Gelidium cartilagineum in CaHfornia 

 reaches a peak in June. Harvesting has also to be carried out with 

 some care so that the algae are given an opportunity to regenerate. 



Apart from its use for the culture of micro-organisms, agar has a 

 variety of other uses. Among these can be included the canning of 

 fish, the sizing of fabrics, in paper and glue manufacture, to add 

 gloss and stiffness to leather, in cosmetics and medicines and as a 



