Tribonemacece 



2f>r> 



compounds. Vegetative division does not occur. Asexual repro- 

 duction takes place by the division of the cell-contents to form 

 ellipsoidal aplanospores, or to form eight ovoidal zoogonidia with 

 two cilia. In those 

 species which are at- 

 tached the zoogonidia 

 generally come to rest 

 on the rim of the empty 

 tube-like cell and there 

 grow into adult cells. 

 A repetition of this pro- 

 cess produces a curious 

 branch-system. Some- 

 times the zoogonidia 

 develop on the apices 

 of other cells which 

 contain the cell-con- 

 tents. No gametes have 



been observed. The Fi S- 12 0- A > Ophiocytium majus Nag., from 



Bowness, Westmoreland. B G, 0. cochlrare 



genus was monographed (Eichw.) A. Br., from same locality. H aud I, 



O. bicuspidatum (Borge) Lemm. forma longispina 

 Lemrn. , from Pilmoor, N. Yorks. J, O. Arbii?.- 

 rulii (A. Br.) Babenh., from Mitcham Common, 

 Surrey. (All x 450.) K, 0. yraciliceps (A. Br.) 

 Babenh., after treatment with potassium hydrate 

 (after Bohlin, x 570). 



Several species are widely distributed in the British Islands. 0. Arbuscula 

 (A. Br.) Rabenh. is an attached species, often with very pretty branch- 

 systems; diam. of cells 3 8/z; fig. 120 J. 0. majus Xag. is the largest 

 species, the cells reaching a diameter of 17 fj. ; fig. 120 A. 0. cochleare (Eichw.) 

 A. Br., 0. capitatttm Wolle, 0. l>i<-tixi>t<.l<it>tin (Borge) Lemm. and 0. parrel nn, 

 (Perty) A. Br. are also frequent species. 



Genus Tribonema Derbes & Solier, 185G. [Conferva in the 

 sense used by Lagerheim, 1888.] The plants of this genus are 

 simple filaments of cylindrical or slightly barrel-shaped cells with 

 strong cell-walls. The latter are often of considerable thickness 

 and the filaments frequently break up into H -pieces. Each 

 H-piece consists of a transverse cell-wall with a cylindrical piece 

 on either side, and the whole is composed of a number of layers of 

 pectose compounds. Each cell is thus bounded by the halves of 

 two H -pieces. The cells contain one (or sometimes two) nuclei 

 and a variable number of parietal chromatophores. In some 

 1 Lemmermann in Hedwigia, Bd xxxviii, 1899, pp. 20 38, t. iii & iv. 



by Lemmermann 1 , but 

 the validity of the thir- 

 teen species he puts 

 forward is questionable. 



