FUCOIDE^E. 



British Genera. 

 Air-vessels stalked. 



[ 337 1 



FUCOIDE^E. 



Sargassum. Branches bearing ribbed 

 leaves ; air-vessels simple. 



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. 



Cystoseira, Root scutate. Frond much 

 branched, bushy. Receptacles cellular. 



Pycnophycus. Root branching. Frond 

 cylindrical. Receptacles cellular. 



Fucus. Root scutate. Frond dichotomous. 

 Receptacles filled with mucus, traversed by 

 jointed threads. 



HimantJialia. Root scutate. Frond cup- 

 shaped. Receptacles (frond-like) very long, 

 strap-shaped, dichotomously branched. 



FtJCOrDEJB, or MELANOSPORE.E. 

 An order of Algae, deriving their ordinary 

 name from the Fucus or Wrack, one of the 

 most common genera of the family. They 



E resent many remarkable points of difference 

 :om 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 Confervoideee. The Fucoids are exclu- 

 sively marine, and are at once distinguished 

 by their olive or dark-brown colour; and 

 although 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 

 occasionally drawn up from deep water prove 

 that this exposure is necessary for healthy 

 growth, by their w r eak structure and the 

 absence of fructification. Some of them 

 are also provided with air-bladders, which 

 maintain them floating 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- 

 wrack (Fucus vesiculosus, fig. 252) ; and still 

 more so in the celebrated Gulf-weed (Sar- 

 gassum bacciferuni), 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 

 structure, of somewhat conical form, cleav- 

 ing, 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 Laminaria- 



ceae, it is composed of a number of stout, 

 super] acent, 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 

 (Elachistece and Myrionemata). Several are 

 of minute size, but very few strictly micro- 

 scopic. Almost all present three regions, 

 resembling respectively the root, stem, and 

 leaf or leaves of the higher plants, although 

 they are not ordinarily regarded as the 

 morphological analogues 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. 



The 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 phenomena 

 presented by what at first appear like iden- 

 tical structures. We have here, as in the 

 Floridea, three distinct form s 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 ECTOCABPUS, 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 ulti- 

 mately converted into zoospores. These en- 

 larged cells are called by Thuret sporanges, 

 and are commonly described as spores in 

 algological works ; but they burst and dis- 

 charge the numerous microscopic zoospores, 

 which are pear-shaped, with a clear, beak- 

 like, narrow end, of olive colour, and have 

 two cilia, not arising from the beak, but 

 from a reddish point on the coloured por- 

 tion ; one cilium is longer than the other, 

 and directed forwards ; the other is short, 

 and trails behind like a kind of rudder. 

 Their movements are very active ; and they 

 seek the light. When they germinate, they 

 become immovable and spherical, acquire 

 a membranous coat, and emit a tubular pro- 

 longation, which soon becomes divided by 

 cross septa, and is developed into a new 



