SIPHONOCLADIALES 



79 



that of the related genus Urospora has been recorded for Rhizo- 

 clonium lubriciim. Urospora is of interest because the zygote first 

 produces a Codiolum stage (so called after the alga it resembles), 

 which is considered to be diploid, and this gives rise to zoospores 

 from which the normal filaments develop, so that if this interpre- 

 tation of the life history is correct we have here another rare 

 example of alternation of morphologically dissimilar generations in 

 the Chlorophyceae. 



*Valoniaceae : Valonia (after the Valoni, an Italian race), "Sea- 

 Bottle". Fig. 54. 



In this genus, which is restricted to warm waters, the young 

 coenocyte consists of one large vesicle whilst the old one becomes 



^(^:^ 



Fig. 54, Valonia. A, young plant of V. ventricosa. B, young plant of V. utricu- 

 laris { X i -4). C, adult plant of same, m = marginal cell. D, plant of V. macrophysa 

 ( X 0-8). E, rhizoid of V. utricularis. F, rhizoids from marginal cells at base of 

 vesicle of V. ventricosa. G, single marginal cell and rhizoid (r) of V. ventricosa. 

 H, V. utricularis fruiting. I, V. utricularis, germinating swarmer. (B, D, after 

 Taylor; rest after Fritsch.) 



divided up into a number of multinucleate segments. It has been 

 suggested (cf. p. 280) that it should really be regarded as a coeno- 

 cytic wall enclosing a fluid, but this interpretation leads to diffi- 

 culties. In some respects, therefore, the genus provides a link with 

 the Siphonales. The macroscopic club-shaped vesicle is attached 

 to the substrate by rhizoids of various types. There is a lobed 



