20 FT'CACEiE. [Thallogens. 



Order III. FUCACEJE.— Seaweeds. 



PhySMB, hn.ll. Om. Bupp. iii p. 19. (1843).— Aplosporei, Decaisne in Ann. Sc. Nat. 2*er. 17, 305. 



] ), IQ508I3. Cellular or tubular asymmetrical bodies, multiplied by simple spores formed 



externally. 

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

 approaching closely to Confervas. Frond either mono- 

 siphonons, consisting of a single cell, which is sometimes 

 uninterruptedly branched, or more commonly polysiphon- 

 ous, ((imposed 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 into a sort of trunk and leaflike blade. 

 Mode of growth by division of the cells; of branching by 

 lateral increase or a vague proliferousness. Mode of propa- 

 gation by spores, contained in superficial cells, which are 

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

 iliiit 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 branches), sometimes on a pecu- 

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

 dlicker.) 

 The reproductive bodies of these plants distinguish them 

 ^° from others of the alliance. In the words of Decaisne 

 r •■ lhoy are simple, and result neither from a modification of 

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

 cell ; their structure is quite peculiar. In the beginning they 

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

 i v j 1 1. c ] ose 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 surface of a 

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

 frond as in Confervas; and if in Seaweeds 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 integumentof Seaweeds. 

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

 are simple or joint. d, thread-shaped or dilated, or more or less filled with 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, indeed, 

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

 a Cystoseira | Acinaria) bears 545,000 male flowers and 1,7'28,000 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 two sorts of fructi- 

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

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

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

 called / n systemata Alga/rum hodi I '/venaria (p. 8,) in which the reader will find 



abundant criticism of the views of Kiitzing and others concerning the Algal alliance. 



M. Decaisne Beems also to have altered his opinion upon this subject, for (ComptCS 

 R »<//.. Nov. 11, 1844,) he and M. Thuret now describe what they suppose to be 

 m \ual organs in Fucus Berratus, and other species, to which they even apply the Linnean 

 - Monoecious and Dioecious. Tiny describe the coneeptacles of the males as being 

 filled with articulate.! filaments bearing numerous antheridia in the form of vesicles con- 

 taining red granule* . ° These antheridia are expelled by the orifice of the coneeptacles ; 

 ii' we examine them with a microscope, we see issue from one of their extremities trans* 

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

 bodii a is furnished with very thin cilia, l>y means of which it moves with very great 



1 Ml I. l!:itr:irliospprniHtn moniliforme ; 2. portion of a branch ; 3 summit of a branch, bear- 

 ing s> on tei of ipon D • lime.] 



