106 USES IN THE ARTS. 



and even yellowish-white before it altogether ceases to 

 vegetate. Similar changes may be observed in many 

 other common species, especially in Ceramium rulrwn, 

 and Laurencia pinnatifida. Light does not always act 

 as a destroyer of colour among these plants in some 

 tribes it affects them by darkening the purples into 

 browns, as in the Polysiphonice. Among these, P. fasti- 

 giata, which grows parasitically on Fucus nodosus, in 

 places where it is exposed to the air for several hours 

 every day, assumes the dark brown of a member of the 

 olive-group. Mere colour, therefore, may lead the stu- 

 dent into error, if he decide solely by it, to the neglect 

 of peculiarities of structure and fructification. 



Several of the Rhodosperms are in different countries 

 either employed as articles of food or used in the arts, 

 in the manufacture of strong sizes and glues. Their 

 nourishing principle appears to reside in a peculiar 

 compound found in several kinds, to which the name 

 Carrigeenin has been given by the chemists. It was 

 first extracted, as the name imports, from Chondrus 

 crispus, the Carrigeen of our coasts, a plant which may 

 be collected to an unlimited extent on all rocky parts of 

 the British shores. The fronds, properly prepared by 

 drying, will keep for any length of time, and a strong 

 jelly may be extracted, when required, by simply boiling 

 in water. Similar jellies are yielded by other species of 

 Chondrus, as well as by the Gigartince, Gracilarioe, and 

 certain Gelidia, some of which yield mucilages of so 

 great strength as to be employed as glue. There have 

 recently been imported into this country samples of an 

 Eastern species, Gracilaria spinosa, which, under the 



