492 POLYMORPHISM AND LIFE-HISTORY IN THE DESMIDIACE^, 



var. serratum Playf., and var. de7iticulatu7n{V\siyi.) G. S. West. 

 Why not apply this same rule to the other genera 1 



Doc. TRABECULA var. Delpontei inihi, formte. (Pl.xi,, f.7). 



Long, semicell. per ordinem deorsum 210, 133, 133, 162, 180, 

 162, 140, 310,.. 



Slide 110a. 



The lengths of the semicells A, A, viz., 2lO/x and 310/. respect- 

 ively, show that the original cell was not complete when the 

 first division took place. 



EXPLANATION OF PLATES XL -XIV. 

 Plate xi. 



Fig.l. — Doc. trahecula Ehr.(b) + var. fruncatum (Breb.)(a) (x23*2). 



Fig.2.— ,, \&i-. truncatum(Br:6h.) {x2S2). 



Fig. 3 — The same dividing ( x 232), 



Fig.4. — Doc. trabecula — form with square base — outgrowth of fig.5 (x34:7). 



Fig.5.— ,, var. Farquharsonu(Roy) ( x 347). 



Fig.6. — ., var. oraiwn, n.var. ( X 347). 



Fig. 7. — ,, y&v. Del2)ontei mihi {x 116). An example of double 



division, a phenomenon which is very common but not very often 

 seen, as the chain of cells necessarily breaks up very easily. A,A, 

 the original semicells; B,B, the semicells formed at the first divi- 

 sion; C,C, and D.D, semicells formed at the second division. 



Fig. 8.— -Doc. trabecula var. diadeiiiatum, n.var. ( x 232). 



Fig. 9. — Doc. trabecula more advanced in growth (x347). 



Fig. 10. — ,, var. £'/ire>i&erg'u(Breb.) ( X 347). 



Fig.n. — ,, var. constrictum, n.var. (x347). 



Fig. 12. — ,, var. Z)eZ/)o?(iei mihi ( X 347). 



Fig. 13. — ,, var. c?-e7!'M;ai!w7t(Roy & Bissett) ( x347). 



Figs. 10-13 are four forms found side by side in a wiount made from a 



single mucilaginous growth of desmids. They serve to show the develop- 

 ment of var. Ehrenhergii into var. crenulatttm. 



rig.l4. — Doc. trabecula '<!&v. Del^^oiitei i. constricta, n.f. ( x 347). 



Figs. 15-16. — Doc. trabecula var, maximum Reinsch, Australian forms 

 ( x 232). 



Figs,17-21, — Various forms of apex in Doc. trabecula vav. Delpontei mihi 

 ( x 463). 



