20 



rUCACE^E. 



[Thallogen:; 



Order III. FUCACE.E.— Seawracks, 



Phycese, Endl. Gen. Supp. iii. p. 19. (1843).— Aplosporeae, Decaisne in Ann. Sc. Nat. 2ser. 17, 305. 

 Diagnosis. — Cellular 07- tubular unsymmetrical bodies, multiiolied by simple spores formed 



externally. 

 Plants sometimes inhabiting fresh water, bvit more frequently salt water ; the former 

 1 approaching closely to Confervas. Frond either mono- 



siphonous, consisting of a single cell, which is sometimes 

 unmterruptedly branched, or more commonly polysiphon- 

 ons, composed of several cells, various in form, placed one 

 above the other, or interwoven, barked or barkless, jointed 

 or continuous, thread-shaped, or of various figures, and not 

 uncommonly divided mto a sort of trimk and leaflike blade. 

 IMode of growth by di\asion of the cells ; of branching by 

 lateral increase or a vague proliferousness. Mode of propa- 

 gation by spores, contained in supei^ficial cells, which are 

 often bladdery (and called Vesicles), growing smgly out of 

 thin colouring matter, consisting of a single nucleus clothed 

 by its proper cellular membrane (or epispore), and dis- 

 charged by the opening of a transparent mother cell (or 

 perispore). Vesicles (or original mother cells) scattered 

 through the whole frond, or seated in particular parts of it, 

 (often the points of the bi-anches), sometimes on a pecu- 

 liar receptacle, naked, or supported by small branches. — 

 {Endlicher.) 



The reproductive bodies of these plants distinguish them 

 from others of the alUance. In the words of Decaisne 

 " they are simple, and result neither from a modification of 

 green matter, nor from its concentration in a pre-existmg 

 cell ; their structure is quite pecuhar. In the beginnmg they 

 are little warts, invested by a very thin membrane, placed 

 close over an inner sac filled with green granules." (The black 

 or brown colour assigned to them by Mr. Harvey is a mistake arising out of imperfect 

 observation.) '^ All the spores are external, that is to say, inserted on the sm-face of a 

 vesicle upon which they are generated. They are never found in the interior of the 

 frond as in Confervas ; and if in Seawracks they can be compared, in consequence of 

 their being contained in a common chamber or' conceptacle, to the spores of certain 

 Rosetangles, it can only be to the corpuscles enclosed in the organs named Ceramidia 

 by the younger Agardh, which however never have the double integument of Seawracks. 

 In most of the latter the spores appear at the base of certain flocks or filaments, which 

 are simple or jointed, thread-shaped or dilated, or more or less filled ^^'ith green matter ; 

 these flocks are wanting however in the greater part of the Dictyotidse, and their use is 

 wholly unknown. There is no reason to suppose them male organs." Decaisne, mdeed, 

 in one place, treats as an absurdity Donati's calculation that a single individual of 

 a Cystoseira (Acinaria) bears 545,000 male flowers and 1,728,000 females. 



The younger Agardh, however, has within a few months expressed his deliberate 

 opinion that in the Rosetangles (his Floridese) organs analogous to sexes are present. 

 " I am very much inclined," he says, « to adopt the opinion that the tv.-o sorts of fructi- 

 fication observable among them are the first attempts at the agency which in higher 

 plants perform the office of sexes, without however having their qualities established, and 

 each capable of producing a new plant without the aid of the other." See his pamphlet 

 ca\\e(iln systemata Algarumhodierua Adversaria {^.^,) in which the reader \\\\\ find 

 abundant criticism of the ^dews of Kiitzmg and others concerning the Algal alliance. 



M. Decaisne seems also to have altered his opinion upon this subject, for (Comptes 

 Rendus, Nov. 11, 1844,) he and M. Thuret now describe what they suppose to be 

 sexual organs in Fucus serratus, and other species, to which they even apply the Linnean 

 names Monoecious and Dioecious. They describe the conceptacles of the males as being 

 filled with articulated filaments bearing numerous antheridia in the form of vesicles con- 

 taining red granules. « These antheridia are expelled by the orifice of the conceptacles ; 

 if we examine them with a microscope, we see issue from one of their extremities trans- 

 parent somewhat pear-shaped bodies, each enclosing a red granule. Every one of such 

 bodies is furnished with very thin cilise, by means of which it moves with very great 



Fig. VIII. 



Fig. VIII.— 1. Batiachospermum moniliforme 

 ing a cluster of spores. (Decaism.) 



2. portion of a branch ; 3. summit of a branch, bear- 



