Order I. Algae, DC.—Algals.

Botanical name: 
Algae

Fig. 146. Esculent Sea Weeds. Algales, Lindley.

Characters.—Cellular flowerless plants, nourished through their whole surface by the medium in which they vegetate; living in water or very damp places; propagated by zoospores, coloured spores, or tetraspores.

Properties.—None of the plants of this order are poisonous. Some of them are nutritious, emollient, and demulcent: these properties they owe to the presence of mucilage [On the Mucilage of the Fuci, with Remarks on its Application to economical ends, by Mr. S. Brown, Jr., in Jameson's Edinb. New Phil. Journ. vol. xxvi. p 409, 1839.] (carrageenin), starch, sugar (mannite), and a little albumen. The peculiar mucilage of sea-weeds will be more fully noticed hereafter (see Chondrus crispus). It differs, says Dr. Stenhouse, from ordinary gum, for, when digested with nitric acid, it yields oxalic, but neither mucic nor saccharic acids.

Mannite is probably obtainable in greater or less quantity from most if not all sea-weeds. It was procured from eight out of nine species examined by Dr. Stenhouse [Memoirs and Proceedings of the Chemical Society of London for 1844.]. He could not detect it in Ulva latissima. The following is a list of the Algae which he examined, arranged in order, according to the quantity of mannite which they severally yielded:—

1. Laminaria saccharina (12.15 per cent. of mannite).
2. Halidrys siliquosa (5 or 6 per cent.).
3. Laminaria digitata.
4. Fucus serratus.
5. Alaria esculenta.
6. Rhodomenia palmata (2 or 3 per cent.).
7. Fucus vesiculosus (1 to 2 per cent.).
8. Fucus nodosus.

On the first two of these plants, when dried, the mannite often forms crystalline incrustations, which by some have been erroneously supposed to be common salt. Dr. Stenhouse thinks that mannite might be more economically procured from sea-weeds than from manna.

The alterative and resolvent virtues ascribed to sea-weeds, and their presumed beneficial effects in scrofulous affections and glandular enlargements, are referable to the inorganic constituents; such as iodine, bromine, the phosphates, and the alkaline substances. The following table shows the composition and proportion of ash in certain sea-weeds:—


 Laminaria saccharina. North Sea. Fucus serratus. North Sea. Laminaria latifolia. Furcellaria fastigiata. Chondrus crispus. Iridaea edulis. Polysyphonia elongata. Delesseria sanguinea. Fucus digitatus. From the mouth of the Clyde. Fudus nodosus. From the mouth of the Clyde. Fudus serratus. From the mouth of the Clyde. Approximate mean.
Potash 24.77 16.02 16.91 21.36 18.00 23.42 21.23 13.72 22.40 10.07 4.51 17.50
Soda 1.84 6.01 .. 24.77 19.47 16.06 5.06 21.34 8.29 15.80 21.15 12.70
Lime 6.50 7.05 8.28 6.02 7.11 10.23 2.92 2.30 8.79 10.98 11.09 7.39
Magnesia 8.13 7.59 6.80 11.04 11.80 .. 20.56 5.94 7.44 10.93 11.66 9.89
Chloride of sodium 33.72 38.72 26.92 .. .. 1.66 13.85 .. 28.39 20.16 18.76 16.56
Chloride of potassium .. .. 10.18 .. .. .. .. .. .. .. .. 0.93
Iodide of sodium 4.70 0.27 .. .. .. .. .. .. 3.62 0.54 1.33 0.95
Phosphate of lime 8.41 4.95 12.80 3.96 0.76 23.23 2.99 3.90 5.63 3.34 9.67 7.24
Phosphate of iron 0.75 0.64 .. .. .. .. .. .. .. .. .. ..
Oxide of iron .. .. .. .. .. .. .. .. 0.62 0.29 0.34 0.24
Oxide of manganese .. .. .. 0.22 .. .. .. .. .. .. .. ..
Sulphuric acid 10.60 18.35 12.63 32.63 42.86 25.19 28.66 40.42 13.26 26.69 21.06 24.76
Silica 0.58 0.40 0.69 .. .. .. 2.83 12.38 1.56 1.20 0.43 1.82
100 [1] 100 [1] 95.21 [2] 100 [2] 100 [2] 99.79 [2] 98.10 [2] 100 [2] 100 [3] 100 100 [3] 99.98
Per centage of ash in weed dried at 212° F. 9.78 25.83 13.62 18.92 20.61 9.86 17.10 13.17 20.40 16.19 15.63 16.46

[1. Schweitzer.] [2. Forchhammer.] [3. Gödechens, Annal. der Chemie und Pharm. liv. p. 352.]

The presence of so large a proportion of potash and phosphoric acid in plants growing in seawater, which contains so small a proportion of these ingredients, is very remarkable. There is reason, however, to believe that the quantity and constitution of the ash are liable to very considerable variation, depending on the locality, season, age of the plant, &c. A vermifuge property has been ascribed to some algals.

Laennec [Treat. on Diseases of the chest, by Dr. Forbes, p. 369.] tried the influence of an artificial "maritime atmosphere" (air impregnated with the vapour of fresh sea-weed) on consumptive patients, and was impressed with an idea of its efficacy; but experience has not confirmed his favourable opinion of its beneficial influence; moreover, the inhabitants of sea-coasts, like those of inland districts, are the subjects of phthisis.

The Elements of Materia Medica and Therapeutics, Vol. II, 3th American ed., was written by Jonathan Pereira in 1854.