370 



Conjugate 



spirostriolatum and P. spirostriolatiforme the cell-wall may contain several 

 girdle-bands of different generations, the greatest number occurring in the last- 

 named species, which is so far known to occur only in Ceylon (W. & G. S. W., 



Fig. 232. I, diagrammatic scheme depicting four generations (A, B, C and D) in the usual 

 type of Closterium', s, s 1? s 2 and s 3 refer to the semicells of successive generations. II, 

 similar scheme depicting three generations of the type of Closterium which develops a girdle- 

 band ; A, B and G, cells of successive generations immediately after cell-division; A*, B* 

 and C*, corresponding generations after development of girdle-bands ; s, sj and s% refer to 

 semicells, and g, g\ and g 2 to girdle bands of successive generations. Ill and IV, Closterium 

 turgidum Ehrenb. var. giganteum Nordst., xl200; IV, surface view of the median part of 

 the cell ; III, longitudinal section of same ; r, the ' ring-furrow ' in the middle of the cell ; 

 t and t', short transverse segments of cell-wall, resulting from cell-divisions, showing the 

 bevelled sutures. (All modified from Lutkemiiller.) 



'02). The girdle-bands (or intercalary bands) are not comparable with those 

 of Diatoms (consult p. 119). 



Asexual reproduction takes place very occasionally by the formation of 

 aplanospores (fig. 233 E G and H J). 



