468 POLYMORPHISM AND LIFE-HISTORY IN THE DESMIDIACE^, 



standing in a weak light. On examination, the living cells were- 

 found to be yellow, incrassate, strongl}' scrobiculate, and in some 

 cases even granulate; whilst the cells originally dead, of which 

 there were a considerable number, I'emained unaltered, with a 

 faintly scrolnculate liyaline membrane. This breadth of trahecula 

 corresponds to trii.ncatuni f. gracilior Richter. 



Doc. TRABKCULA Ehr., forma. (Pl.xi., f.4). 



Forma parte inferiori semicellularum cylindracea; lateribus 

 parallelis, sursum ad apices rapide convergentibus; apicibus rugis 

 circ.l2(visis 7) ornatis. Long. 346; lat. bas.44; centr.40; ap.21/i. 



Guildford(78). 



This is the outgrowth of var. Farquharsonii(Roj). 



Var. FARQUHARSONii(Roy). (Pl.xi., f.5). 



Long.200; lat. bas.55; centr.51; ap.24M. 



Botany(109). 



Cf. W. ctG. S. West, Monog. Brit. Desm. PLxxix., f.6. 



Var. BREFELDii(Istvanffi), f. gracilior. (Pl.xiii., f.23a). 



Forma gracilior; apicibus late-rotundatis. Long. semi. 67; lat. 

 bas.30; max. 38; ap.20/x. 



Auburn. Cum var. trwicato. 



Cf. IstvanfB, Felso-raagyar. tozeg. megvizs. T.ii., f.35. 



Develops into var. truncatnm. Compare Pl.xi., f.3, the two 

 inner semicells. 



Var. TRUNCATUM(Breb.). (Pl.xi., Lla,2,3a), 



Long.l70-22S; lat. max.37-45; ap.18-20^. 



Auburn(57, 67, 70, 8.5, lOt, etc.). 



When the heat causes the large forms of Doc. trahecula to- 

 divide repeatedly, they descend greatly in size and shape(c/.P]. xi., 

 f.7). These degraded forms, howevei', gradually pull themselves 

 together, and var, truncatum is the result. It is the lowest form 

 of Doc. trahecula, with the exception of var. ^re/e/f/u'(Istvanffi), 

 Pl.xiii., f.23«, and allied shapes like vai-. crasaum Boldt(Sibir.. 



