The figure (20) in the plate was drawn from a conceptacle of _Fucus serrátus_, another common species, differing from _F. vesiculosus_ in having the margins of the frond serrate; the antheridia of the two species do not, however, differ in any important respect. To examine the conceptacles of _Fucus_ and their contents, the receptacles should be soaked in water, if not fresh, and thin sections made with a sharp knife. They form very beautiful objects, and may be preserved in chloride of calcium or glycerine. FLORID´EÆ, or Rhodosper´meæ (ῥὁδον, rose, σπἑρμα, seed).--The second Order of Algæ, forming the Florideæ (_flos_, a flower), comprises the red sea-weeds; a few of them are purple, or greenish-red; so that by the colour alone they may be readily distinguished from the Fucoids, and from nearly all those of the next Order, the Confer´voids. A few of them are leaflike, or possess flat fronds; but most of them consist of finely divided or feathery fronds. They are often found upon the sea-shore of a dirty white colour, the colouring matter having been decomposed or washed out by rain. We shall consider a few of the genera and species under the heads of the families to which they belong. CORALLINA´CEÆ, the Corallines, or calcareous Algæ.--In this family we have the beautiful _Corallína officinális_ (Pl. IV. fig. 28), the common Coralline, which is very abundant on the sea-shore, attached to larger sea-weeds, shells, and rocks. It is hard and chalky, from the presence of a large proportion of carbonate of lime in its minute cells. The fronds are composed of jointed and branched filaments. The fructification (figs. 29 and 30) consists of ovate cellular capsules, or _ceramid´ia_ (κερἁμιον, earthen vessel), placed mostly at the ends of pinnate stalks, and containing a tuft of somewhat club-shaped jointed spores, springing from the base of the capsules (fig. 30). When ripe, the spores escape from a pore or hole in the end of the capsules. The spores are 4-jointed, and hence are called _tet´raspores_ (τἑτρα, _four_). To observe these spores, the capsules must be soaked in strong vinegar for some hours, and then washed with water, to dissolve the calcareous matter. _Jánia rúbens_ (Pl. IV. figs. 7 and 8) is another common and very elegant little coralline, and is of a pale red colour. It differs from the last in the branches being dichot´omous (δἱχα, in two, τομὀς, cutting) or forked, instead of pinnate. The capsules, or ceramidia, have also two short horn-like branchlets, placed one on each side, near the end. The genus _Melobésia_ has the frond crustaceous, _i. e._ forming a hard crust or layer. _M. polymor´pha_ (Pl. IV. figs. 5 and 6) is common on shells, stones, &c. The capsules (ceramidia) here form little blunt cones, scattered over the crusts, and containing the tufted tetraspores, as in _Corallina_.