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MUL TJNUCLEA T.£ 283 



often strongly encrusted with calcium carbonate. In several of the 

 genera of Siphonocladaceae, but little is at present known as to the mode 

 of reproduction ; and until this has been more fully ascertained, their 

 true affinities are uncertain ; and it is possible that the order, as at 

 present constituted, includes forms which are not nearly allied to one 

 another. In none of the genera is a fertilisation of oogones by anthero- 

 zoids known, similar to that of Vaucheria. The ordinary mode of re- 

 production appears to be by zoospores which germinate directly without 

 conjugation. Other modes of non-sexual propagation occur in some of 

 the genera, by 'propagules' or by ' prolification.' The following are 

 some of the more remarkable forms included in the group. 



The Caulerpe^ include the single genus Caulerfa Lmx., cha- 

 racterised by its greatly-branched thallus of 

 remarkably leaf-like appearance. Very little is 

 known about the mode of reproduction. The 

 ordinary process of propagation appears to be 



by ' prolification ' from all parts, the so-called -^ s*. * <ai^) 



' roots,' ' stem,' and ' leaves.' Within the tube 

 are solid branched layers of cellulose stretching 

 from wall to wall, and forming a closed net. It l^'i tit 



often covers enormous tracts of the shore Ve ■^j 



between high and low water marks with a green • "■ it '^ 



coating. \ / 



The Valoniace^ (Valonia, Gin., Siphono- 

 cladus, Schr., Struvea, Sond., Anadyomene, 

 Lmx., &c.) are an ill-defined family, in which , 



the cell is frequently swollen up into a bladder- i_ 



like structure ; the mode of propagation is ap- viQ.'isi.-V'^ionia.macrothysa 

 parently by non-sexual zoospores. To these HauckT'"'"' ''^^'' *^*^^" 

 are closely allied the Udoteace^ (Avrainvillea, 



Dene., Penicillus, Ktz., Udotea, Lmx., Halimeda, Lmx.^ &c.). Halimeda 

 has a remarkable Opuntia-like appearance, from the single cell consisting 

 of a large number of pear-shaped branches, each connected with the 

 one below it by a narrow base, and the whole encrusted by calcium 

 carbonate. 



In the Bryopside^ (Bryopsis, Lmx., Derbesia, Sol.) and Spon- 

 GODiE^ (Codium, Stackh.) the thallus is not encrusted with calcium 

 carbonate. Codium forms a spongy spherical or cylindrical floating mass, 

 of considerable size, consisting of branched tubes. It is apparently pro- 

 pagated by zoospores. In Bryopsis Lmx. the thallus has a branched 

 root-like colourless portion, and an erect cylindrical stem, the upper half 

 of which branches into pinnate leaf-like ramifications with limited apical 



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