The simpler brown seaweeds, so far as known, multiply only by means of zoöspores, which may grow directly into new plants, or, as has been observed in some species, two zoöspores will first unite. A few, like _Ectocarpus_ (Fig. 28, _A_), are simple, branched filaments, but most are large plants with complex tissues. Of the latter, a familiar example is the common kelp, "devil's apron" (_Laminaria_), often three to four metres in length, with a stout stalk, provided with root-like organs, by which it is firmly fastened. Above, it expands into a broad, leaf-like frond, which in some species is divided into strips. Related to the kelps is the giant kelp of the Pacific (_Macrocystis_), which is said sometimes to reach a length of three hundred metres. [Illustration: FIG. 28.--Forms of brown seaweeds. _A_, _Ectocarpus_, × 50. Sporangia (_sp._). _B_, a single sporangium, × 150. _C_, kelp (_Laminaria_), × ⅛. _D_, _E_, gulf weed (_Sargassum_). _D_, one-half natural size. _E_, natural size. _v_, air bladders. _x_, conceptacle bearing branches.] The highest of the class are the gulf weeds (_Sargassum_), plants of the warmer seas, but one species of which is found from Cape Cod southward (Fig. 28, _D_, _E_). These plants possess distinct stems and leaves, and there are stalked air bladders, looking like berries, giving the plant a striking resemblance to the higher land plants. CHAPTER VII. CLASS III.--THE RED ALGÆ (_Rhodophyceæ_). These are among the most beautiful and interesting members of the plant kingdom, both on account of their beautiful colors and the exquisitely graceful forms exhibited by many of them. Unfortunately for inland students they are, with few exceptions, confined to salt water, and consequently fresh material is not available. Nevertheless, enough can be done with dried material to get a good idea of their general appearance, and the fruiting plants can be readily preserved in strong alcohol. Specimens, simply dried, may be kept for an indefinite period, and on being placed in water will assume perfectly the appearance of the living plants. Prolonged exposure, however, to the action of fresh water extracts the red pigment that gives them their characteristic color. This pigment is found in the chlorophyll bodies, and usually quite conceals the chlorophyll, which, however, becomes evident so soon as the red pigment is removed.