=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. =385. Order Cryptonemiales.=—Examples are Dudresnaya, Melobesia, Corallina, etc., the last two genera include many species with a wide distribution. Class Charophyceæ, Order Charales. =386.= The Charales are by some thought to represent a distinct class of algæ standing near the mosses, perhaps, because of the biciliate character of the spermatozoids. There is one family, the Characeæ. The plants occur in fresh and brackish water. Aside from the peculiarity of the reproductive organs they are remarkable for the large size of the cells of the internodes and of the “leaves,” and the protoplasm exhibits to a remarkable degree the phenomenon of “cyclosis” (see paragraphs 17-20). Three of the genera are found in North America (Chara, Nitella (Fig. 8) and Tolypella). [Illustration: Fig. 172_a_. Reproductive organs of _Chara fragilis_. _A_, a central portion of a leaf, _b_, with an antheridium, _a_, and a carpogonium, _s_, surrounded by the spirally twisted enveloping cells; _c_, crown of five cells at apex; β, sterile lateral leaflets; β′, large lateral leaflet near the fruit; β″, bracteoles springing from the basal node of the reproductive organs. _B_, a young antheridium, _a_, and a young carpogonium, _sk_; _w_, nodal cell of leaf; _u_, intermediate cell between _w_ and the basal-node cell of the antheridium; _l_, cavity of the internode of the leaf; _br_, cortical cells of the leaf. _A_ × about 33; _B_ × 240. (After Sachs.)]