720 SYSTEMATIC BOTANY. 



afford, upon cooling, a colourless, transparent jelly, — thus form- 

 ing ten times more jelly than a like weight of the hest animal 

 gelatine. In order, therefore, to produce a jelly of equal con- 

 sistence, it would be only necessary to employ the tenth part of 

 what is necessary when isinglass is used. Jellies prepared from 

 species of Gelidium, Laurencia, 8fc., are much employed for food 

 in China, Japan, &c. The edible birds' nests of China, so 

 highly valued for food, seem to be constructed by swallows 

 from these, or closely alHed species of Algge. 



In medicine the above-mentioned nutritious Algae may be 

 used for their emollient and demulcent properties. Several 

 species of Algae, particularly Fucus vesiculosus, have been used 

 as remedies in Goitre and scrofulous diseases. They owe their 

 beneficial effects in such cases, principally, to the presence of a 

 small quantity of iodine. The ashes obtained by burning many 

 species of Algse in the open air, form the substance called kelp, 

 which was formerly much used for the preparation of carbonate 

 of soda; but this is now more cheaply obtained from sea-gait. 

 Iodine is, however, still obtained from kelp. Some Algse have 

 been reputed to possess vermifugal properties; none are known 

 to be poisonous. 



Several Algae are remarkable for imparting colours to water, 

 snow, &c. Thus, Protococcus (Palmella) atlanticus gives a red 

 colour to certain parts of the Atlantic ; P. nivalis contributes 

 to communicate a red colour to snow ; and P. viridis, a green 

 tint; Dolichospermim Thompsoni imparts a green colour to the 

 Serpentine and to some Irish and Scotch lakes; the red colour 

 of the Red Sea is also in part attributed to the presence of 

 Trichodesmium erythrceum ; &c. &c. 



Some Algffi are met with in diseased animal tissues. The 

 Achlya prolifera, which attacks the gills of gold fishes, &c., and 

 Sarcimda ventriculi, found in the stomach, &c. of animals, may 

 be enumerated as amongst the most remarkable of such forms. 



Lajninaria. — L. saccharina is remarkable for the large quantity of mannite 

 it contains, upwards of I'i per cent. The young parts of it, mixed with those 

 of L. dt'gilata, are eaten in Scotland, &c., under the name of Tangle. The 

 latter also contains much mannite. L. saccharina is called Sea-tape in China, 

 where it is used for food and other purposes. L. potatorum is used for food 

 in Australia, and other species possess similar properties. 



Alaria escw/fn/a (Bladderlocks, Hen-Ware, or Honey-Ware) contains man. 

 nite. It is employed for food in Ireland, Scotland, Iceland, and other northern 

 regions of the world. 



Fucus Several species contain mannite, as F. vesiculosus, nodosus, and 



serratus. F. vesiculosus. Sea Wrack. — This Alga is much used in winter in 

 certain islands of Scotland for feeding horses and cattle. The expressed juice 

 of its vesicies has been given internally, and frictions of the plant have been 

 employed externally, in glandular and scrofulous affections. The substance 

 called Vegetable Kthiops, which has been used in similar diseases to the 

 above, is a kind of charcoal produced by the incineration of this Alga in close 

 vessels. The beneficial effects in such cases is principally due to the presence 

 of a small quantity of iodine. It was formerly extensively employed in the 

 preparation of kelp. 



