MUL T1NUCLEA T.-E 



289 



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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^E include the single genus Caulerpa 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 

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

 are solid branched layers of cellulose stretching 

 from wall to wall, and forming a closed net. It 

 often covers enormous tracts of the shore 

 between high and low water marks with a green 

 coating. 



The VALONIACE^E (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- 

 like structure ; the mode of propagation is ap- 

 parently by non-sexual zoospores. To these 

 are closely allied the UDOTEACE^E (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^E (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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FIG. 257. Valonia macrophysa- 

 Ktz. (natural size). (After 

 Hauck.) 



