28 SIPHONACE^. 



IV. CODIUM. StoAihh. 



Frond sponge-like (globular, cylindrical or flat ; simple or branched) composed of a 

 plexus of unicellular, branching filaments, filled with green semifluid endochrome. 

 Sporangia lateral, on the ramuli of the filaments (forming the surface of the frond), 

 and containing innumerable zoospores. 



The frond in this genus, though it assumes a well-defined shape, characteristic of the 

 particular species, does not form a solid, compact body as in Udotea, but consists 

 altogether of innumerable slender, unicellular, branching filaments, inextricably inter- 

 laced or woven together. In the centre of the filamentous mass these filaments are 

 threadlike, branching at longish intervals, curled or sinuous, filled with slimy fluid, 

 and only partially supplied with green colouring matter. In the elongated species, as 

 in C. tommtosum, these axial filaments take a longitudinal direction ; in the globose 

 ones they radiate from a central point, as in the singular C. mammillosum of Austra- 

 lia; and in the incrusting species, like C. adhcerens, they spread horizontally over the 

 surface of the rock on which the plant grows. In all cases they throw out more or 

 less club-shaped ramuli, which spread in a direction vertical with the surface of the 

 frond, and their apices lying close together, but not cohering, constitute the periphery. 

 There is no calcareous incrustation as in Udotea, and no false epidermis as in ffali- 

 meda ; but with these exceptions there is much similarity in structure. The external 

 habit is remarkably varied. In C. tomentosum, the type of the genus, and the most 

 widely dispersed species, the frond is somewhat cylindrical, and dichotomously branched ; 

 in a form (or species ?) called C. elongatum a similarly branching frond is extrava- 

 gantly dilated and flattened especially at the axils ; in C. laminarioides a stipi- 

 tate frond suddenly expands into a flat lamina a foot or two across, resembling nothing 

 so much as a piece of green friese-cloth ; in C. amphibium a number of minute papil- 

 liform branches rise from a flat adherent surface ; and in C. adhcerens there is a flat, 

 clothlike crust, destitute of branches, and indefinitely covering rocks and woodwork. 

 In C. bursa the frond is sessile, gradually becoming globose and at length hollow ; and 

 lastly, in C. mammillosum the frond is either exactly spherical or egg-shaped, composed 

 of filaments radiating from a central point, and being, so far as known, destitute of 

 any root-like attachment. 



The fructification in Codium consists of an oblong, ovate sporangium, formed of a 

 single cell, separated from the ramulus near the base of which it is developed, by a 

 diaphragm, and containing, at first, a dense, dark-green endochrome, and finally a 

 multitude of zoospores. These latter are ovate, of a deep green colour, with a minute 

 " rostrum" at one end, which carries a pair of cilia, that serve as organs of locomo- 

 tion till the spore becomes fixed and germinates. This fruit is exquisitely figured by 

 Thuret, in his memoirs on the Zoospores of Algae, in An. Sc. Nat. 3rd Series, Bat. 

 vol. 14, tab. 23, where a full account of the evolution is given. 



