466 POLYMORPHISM AND LIFE-HISTORY IN THE DESMIDIACE^, 



them within that biological subspecies. As might be expected 

 of forms linking two subspecies, the specimens of var. Delpontei 

 vary a good deal in character, specially as regards the apex. The 

 only character that can be unhesitatingly relied upon, is the 

 breadth(basal inflation 30-39^). W. & G. S. West, in their Mon- 

 ograph, have included this variation with the smaller Ehrenhergii- 

 forms. This is quite impossible with Australian specimens. 

 Doc. Ehrenbergii proper here, wliile it has precisely the range of 

 length and breadth given by W. West in Frw. Alg. W. Ire., 

 differs from the British forms in having only one basal inflation 

 at all prominent {never as in Monog., Vol.i., PI. 29, tigs.10-11), 

 and the apex very often quite smooth. Our forms of Delponte'.s 

 Ehrenbergii either lean towards trab. v. crenulatum in having a 

 plicate apex, or it has the apical granules strongly accentuated, 

 generally in shape more like the teeth of Doc. nodosum, quite 

 unlike any other form in the species. 



The case of Doc. bacnlum. — At the outset I had no idea of 

 including baculum in the forms of Doc. trabecula, in considera- 

 tion of its axile chloroplast. In gathering No. 109, however, it 

 was fairly abundant in excellent condition. There was indeed a 

 single chloroplast, but parietal and curved round the semicell 

 into a tube, no pyrenoids at all being present. It seems certain, 

 therefore, that the chloroplast is first axile, with a central row of 

 pyrenoids; but, as the cell develops, the chloroplast becomes 

 parietal, the pyrenoids are absorbed, and the centre of the cell 

 becomes hollow. Finally, the chloroplast splits up longitudinally 

 into three or four jiarietal fillets in which the pyrenoids are 

 reformed. 



The inflated form of baculum, which I figure(Pl.xii., f.2) had a 

 row of decided basal granules; and accompanying it, were cells 

 more like the typical form in Ralfs(Pl.xxxiii., f.5), and W. & G. 

 S. West(Monog., Vol.i., PI. 27, f. 1 ). Of these latter, some had 

 the basal granules replaced by fainter plicae, others had no basal 

 markings at all, and in other cells again, one semicell would have 

 basal plicae and the other granules(Pi.xii., f.3). Moreover, a cell 

 was seen(Pl.xii., f.4), baculoides in shape, but the breadth of 



