248 BRITISH DESMIDIACE/E. 



Sweden. Denmark. Finland. Poland. Central, 

 N., and S. Russia. Greenland. Japan. India. 

 Burma. Australia. New Zealand. Central Africa. 

 Nova Scotia. United States. Colombia. Brazil. 

 Paraguay. 



D. Swartzii is the commonest species of Desmidium. It lias 

 a very extensive distribution, and sometimes occurs in 

 abundance. 



There has been some confusion with regard to the zygospores 

 of this species. Ealfs, in 1848, figured certain spores which he 

 supposed had been formed each from the contents of a single cell. 

 Various other authors have published from time to time figures 

 quite similar to that of Ralfs, under the description of zygospores. 

 Archer in ' Quart. Journ. Micr. Sci.' v. 7, 1867, p. 296, reports 

 that he had observed conjugation in this species, and that Ralfs" 

 figure was quite accurate, but that the earlier observer was wrong 

 in supposing that the spores were formed each from a single cell. 

 Archer states that the conjugating filaments apply themselves 

 so closely to each other that it is very difficult to distinguish 

 that there really are two there. Archer had quite satisfied him- 

 self, however, that this was so. Crowe, in ' Quart. Journ. Micr. 

 Sci.' 1874, p. 105, again supported Archer's statement. Further, 

 Delponte (' Spec. Desm. Subalp.' 1873, t. 2, f. 12) figures spores 

 which he says are formed by the conjugation of two cells, and 

 these are quite similar to those of Ralfs. In view of this evi- 

 dence, together with the fact that if Ralfs' figure represents one 

 filament, and not two, it is of extraordinary large diameter, it 

 seems highly probable that the figures of Ralfs, and similar ones 

 of other authors, may be considered to represent the zygospores 

 of this species, with varying degrees of accuracy, but further 

 corroboration of this is certainly desirable. 



Var. quadrangulatum (Ralfs) Roy. (PI. CLXIII, 



figs. 9, 10.) 



D. quadrangulatii in Ralfs in Ann. Mag. Nat. Hist. 1845. p. 405, t. 12, f. 9 ; 

 Brit. Desm. 1848, p. 62, t. 5 ; Arch, in Pritch. Infus. 1861, p. 723, t. 2, 

 f. 37 ; Rabenh. Flor. Eur. Alg. 1868, p. 155 ; Delp. Spec. Desm. subalp. 

 1873, p. 60, t. 2, f. 21-27 ; Wolle, Desm. U. S. 1884, p. 27, t. 2, f. 13, 14 ; 

 Cooke, Brit. Desm. 1887, p. 11, t. 5, f. 3 ; Comere, Desm. de France, 

 1901, p. 200, t, 16, f. 13 ; Borge, Alg. erst. Regnel. Exp 1903, p. 122, 

 t. 5, f. 24; Hustedt. Desm. et Bacill. Tirol, 1911, p. 342; Borge, .Sao 

 Paulo Alg. 1918, p. 75. 



