FUCACE.E. 



[ 274 ] 



FUCOIDEiE. 



p. 109, id. Sp. Alg. p. 96; Rabenhorst, Die 

 Sussw. Diat. p. 50. 



FUCACE.E. — A family of Fucoideae. 

 Olive-coloured inarticulate sea-weeds, whose 

 reproductive organs are borne in stalked sacs 

 upon the walls of spherical cavities excavated 

 in the substance of the frond. Fructification 

 sporanges or spore-sacs and antheridia. The 

 spores of Fucus divide into two, four or eight 

 within the sac ; those of the other genera 

 remain undivided. The antheridia are filled 

 with spermatozoids (or antherozoids), which 

 in Fucus have been seen to fertilize the 

 spores. See Fucus. 



Synopsis of British Genera. 

 * Air-vessels stalked. 



I. Sargassum. Brawc^es bearing ribbed 

 leaves ; air-vessels simple. 



II. Halidrys. Frond linear, pinnate, 

 leafless ; air-vessels divided into several cells 

 by transverse partitions. 



** Air-vessels immersed in the substance of 

 the frond, or absent. 



III. Cystoseira. Root scutate. Frond 

 much branched, bushy. Receptacles cel- 

 lular. 



IV. Pycnophycus. Root branching. 

 Frond cylindrical. Receptacles cellular. 



V. Fucus. Root scutate. Frond dicho- 

 tomous. Receptacles filled with mucus, tra- 

 versed by jointed threads. 



VI. HiMANTHALiA. Eoo^ scutatc. Froud 

 cup-shaped. Receptacles (frond-like) very 

 long, strap-shaped, dichotomously branched. 



FUCOIDE.E, or MELANOSPORE^.— 

 An order of Algse, derivingtheir ordinary name 

 from the Fucus or Wrack, one of the most 

 frequent genera of the family. They present 

 many remarkable points of difference from 

 the red sea-weeds in their higher forms, 

 while the lowest forms approach the simpler 

 genera of that order and the higher forms of 

 the Chlorosperms. The Fucoids are exclu- 

 sively marine, and are at once distinguished 

 by their olive or dark-brown colour, and al- 

 though some of the larger kinds grow in deep 

 water, the majority are met with on rocks 

 between high and low water mark, where 

 they are exposed to the atmosphere at each 

 efflux of the sea ; those which are dra\Mi up 

 from deep water occasionally prove that this 

 exposure is necessary for healthy growth, by 

 their weak structiue and the absence of fruc- 

 tification. Some of them are also provided 

 with air-bladders, which maintain them float- 

 ing or erect, and with at least their upper 



lobes little beneath the surface of the water. 

 These air-bladders are very well seen in our 

 common Bladder-wTack (Fucus vesiculosus, 

 fig. 256), and still more so in the celebrated 

 Gulf- weed {Sargassum bacciferum), where 

 the stalked berry-like bladders are the most 

 striking feature of the plant. 



All the larger kinds grow on rocks, to 

 which they are attached by a root-like struc™ 

 ture, of somewhat conical form, cleaving 

 like the ' sucker' with which school-boys lift 

 stones, to the rock ; in many this cone is 

 solid, and composed of tough cellular tissue; 

 in others, especially the Laminariacese, it is 

 composed of a number of stout, superjacent, 

 branched cords, growing out of the frond 

 one above another, and attaching themselves 

 to the rock, like the roots of a Tree-fern or 

 a Palm. Some (Pycnophycus) spring from 

 a creeping stem-like portion, spreading in a 

 netted mass over the rocks ; while many of 

 the smaller are parasitical, or more properly, 

 epiphytic, growing on the fronds of the 

 larger kinds, to which they attach themselves 

 by minute 'sucker' -like disks. Some appear 

 to be true parasites (Elachisteee and Myrio- 

 nemata). Several are of minute size, but 

 very few strictly microscopic. Almost all 

 present three regions, resembling respect- 

 ively the root, stem, and leaf or leaves of 

 the higher plants, although they are not or- 

 dinarily regarded as the morphological ana- 

 logues of them. In a few cases the frond is 

 a shapeless mass or crust, lying close to the 

 surface of the rocks. None become calcified 

 like the Corallines. 



T\\Q fructification of these plants is still in 

 a somewhat obscure condition as regards the 

 order in general, for great apparent diversi- 

 ties occur in the physiological phajnomena 

 presented by what at first appear like iden- 

 tical structures. We have here, as in the 

 Floridece, three distinct forms of reproductive 

 structure, known respectively as — 1, zoo- 

 spores ; 2, spores ; and 3, spermatozoids. 



1. The zoospores are the reproductive bo- 

 dies most frequently met with, and in the 

 lower forms the arrangements are not very 

 different from those in the filamentous Con- 

 fervoids. In Ectocarpus, where the frond 

 is composed of jointed cellular filaments, the 

 cells at the ends of the branches, or other 

 articulations, become enlarged and filled with 

 granular matter which is ultimately converted 

 into zoospores. These organs are called by 

 Thuret oosporanges, and are commonly de- 

 scribed as spores in algological w^orks ; but 

 they burst and discharge the numerous mi- 



