Fig. 188.
Section of cystocarp of
rhabdonia, showing spores.
379. Fertilization of the higher red algæ.—The process of fertilization in most of the red algæ is very complicated, chiefly because the fertilized egg-cell (procarp) does not develop the spores directly, as in Nemalion, Lemanea, etc., but fuses directly, or by a short cell or long filament with one or more auxiliary cells before the sporocarp is finally formed. Examples are Rhabdonia, Polysiphonia, Callithamnion, Dudresnaya, etc. ([fig. 189]). The auxiliary cell then develops the sporocarp. See fig. 189 for conjugation of a filament from the fertilized procarp with an auxiliary cell.
Fig. 189.
Dudresnaya purpurifera. tr, trichogyne, with spermatozoids attached; ct, connecting-tube which grows out from below the base of the trichogyne, and comes in contact with the fertile branches f, f; ct′, young connecting-tube. (After Thuret and Bornet.)
380. Uses of the red algæ.—Many species produce a great amount of gelatinous substance in their tissues, and several of these are used for food, for the manufacture of gelatines and agar-agar. Some of these are Gracilaria lichenoides and wrightii, the former species occurring along the coast of India and China. The plant is easily converted into gelatinous substance (agar-agar). Chondrus crispus, widely distributed in the northern Atlantic is known as “Irish” moss and is used for food and for certain medicinal purposes. Gigartina mamillosa in the Atlantic and Arctic oceans is similarly employed. The following orders are recognized in the red algæ:
381. Order Bangiales.—Example, Bangia atropurpurea (= Conferva atropurpurea) in springs and brooks in North America and Europe. Porphyra contains a number of species forming broad, thin, leaf-like purple sheets in the sea.
382. Order Nemalionales.—Including Lemanea, Batrachospermum, Nemalion, described above, and many others.
383. Order Gigartinales.—In this order occurs the common Iceland moss (Chondrus crispus) in the sea, and Rhabdonia and Gigartina mentioned above.
384. Order Rhodomeniales.—In this order occurs Gracilaria and Polysiphonia mentioned above, also the beautiful marine forms like Ceramium.