CHLOROPHYCE^ 137 



atives of multinucleate plants. The British species 

 are Bryopsis hypnoides and B. plumosa, C odium 

 tomentosum, C. Bursa and 0. adhcerens, and Derbesia 

 tenuissima. 



UDOTEACEAE. 



General Characters. - - The reproductive bodies 

 (known only in the case of one genus, Halimeda) 

 are zoospores produced within zoosporangia. It is 

 not known whether they are zoospores or gametes in 

 fact, since no observation has been made of their 

 conjugation. The principal interest in the order is 

 to be found in the vegetative part of the thallus, 

 since the generic forms are not only of striking out- 

 ward appearance, but of singular structure. The 

 cohesion of the filaments composing the fronds is 

 attained by their being interwoven (Avrainvillea), by 

 incrustation of carbonate of lime (Penicillus and 

 Halimeda), or by incrustation more or less partial 

 with the addition of lateral haptera or holdfasts 

 binding the filaments together ( Udotea). 



The Thallus. In Avrainvillea ( = Fradelia, Chloro- 

 plegma, Ehipilia, Chlorodesmis) the frond is of simple 

 structure, consisting of unicellular filaments, re- 

 peatedly branched, and interwoven so as to form a 

 stalked or sessile, fan-shaped, felt-like frond above 

 and a dense mass of rhizoids below. The fan-like 

 fronds are tough and spongy, and often lacerated at 

 the edges. The filaments are dichotomously branched, 

 and each branch is constricted at the base. In some 

 of the species, the whole of the filament is constricted 



