296 PROCEEDINGS OF SECTION D. 



the forms comprising a species, which it is convenient to use as a 

 sub-heading because of the number of variations directly connected 

 with it. Having lately found it necessary, in order to name two 

 simple forms of Doc. coromdakmi, Grun., to make out a complete 

 sciagraphical synopsis of all its variations, I append the result. 

 It will serve to show the lengths to which a true Desmid species 

 runs, to indicate my conception of a sub-species when classification 

 goes by outline, and to point the urgent need that exists for critical 

 revision. The simple fact of all these forms having the same 

 ring of tubercles at the apex is of itself amply sufficient to warrant 

 their inclusion in one species. In this genus the species are 

 broadly defined, the characteristics of each are simple and evident, 

 while the variations are multifarious, run the whole gamut of 

 certain approprate shapes, and admit even the suppression of one 

 or more of the typical elements. In Doc. coronulatum the tubercles, 

 in Doc. Ehr.-trab.-coronatum. the apical granules (or I'ugae), in Doc. 

 nodosum (inch D. constrictum) the verticils of inflations, in D, 

 verrucosum the reticulate scrobiculations — these are the funda- 

 mental points characteristic of the species. The same class of 

 polymorphic forms may be found in every species, viz., inflated, 

 stout, medium, narrow semi-cells and those with undulate sides, 

 and there may be every possible combination of length and breadth 

 within the limits, but none of these indicate any fundamental 

 specific difference. The same is true of Closterimn. 



Every Desmid species holds a certain number of distinct 

 possibilities as regards form, length, breadth and ornamentation, 

 and it is the immense number and variety of the combinations 

 that can be made out of these that is the cause of the vast bulk 

 of the species and the intricate character of its hfe-history — the 

 connection, that is, of its innumerable polymorphic forms. 



Sciagraphical synopsis of the species Doc. coronulatum (Grun.) 

 Lund. : — 



(1). Cells tumid, no basal inflation — 

 Doc. coromdatum Grun., Insel Banka, 1865, T. ii, f. 20. 



var. Willei mihi., PI. coron. var. Caldense Wille, Svdam., 1884, 

 T. I, f. 43. 



var. ligatum (W. & G. S. West), Frw. Alg. Madag., 1894, Plate 

 V, f. 42. 



var. regale (Turn.), Doc. regale Turn., I.e. T. iii, f. 6. 



var. Bengalense (Turn.), D. Bengalense Turn., I.e. T. iii, f. 4. 



var. fmn'um (W. & G. S. \Nesi)^Frw. Alg. Madag., 1894, PI. v, 

 f. 41. 

 (2). Sides undulate. Subspecies alternans. 



var. alternans (Nord.), Desm. Braz. Cehn. 1869, T. in, f. 36. 



var. Caldense (Nord.), Alg. Braz. 1877, T. ii, f. 2. 



(Syn. D. salebrosum Turn., I.e. 1892, T. ii, f. 12) 

 (Syn. D. conjunctum Turn., I.e. T. iv, f. 6) 



va.T. granulatum (Borge), .4/^. Regnell., 1903, T. ii, f. 4. 



var. subalternans (Borge), Trop. u. subtrop., 1899, T. i, f. 12. 



