3l8 THE ALGAE 



colous, crustaceous Ralfsiaceae. Another line of development is 

 provided by the cushion forms which could well have come via 

 plants such as Elachista, The final stage is probably represented by 

 a genus such as Corynophlaea with Petrospongium (see p. 155) being 

 treated as a reduced form. Yet another line of evolution must be 

 represented by the pseudoparenchymatous Spermatochnaceae 

 with apical growth instead of the usual trichothallic. Spermatochnus 

 and Nemacystus with a single axial thread may be regarded as 

 primitive to genera (Stilophora) with several axial threads. Pseudo- 

 parenchymatous development is also found in Chordaria, repre- 

 senting the most advanced condition in the Chordariales, and in 

 the pecuhar monotypic genus Splachnidium. In the latter genus, 

 the unilocular sporangia are borne in sunken pits or conceptacles, 

 very reminiscent of the Fucales. Another pecuhar monotypic genus 

 with no immediate obvious affinities is the antarctic Caepedium. 

 Here there is a basal thalloid plant, reminiscent of Ralfsia, from 

 which at certain times arise branched threads of ChordariaAikc 

 structure. The plant also produces a Leathesia-likQ cushion form. 

 The schema below attempts to indicate the hues along which evolu- 

 tion may have progressed in this order with its fairly wide range of 

 forms. 



Notheiaceae, 

 \ 



(Splachnidiaceae) 

 Splachnidium 



Pseudo- 

 parenchymatous 



\ 



Stilophora 

 (several axial 



threads) Chordaria 



T pseudo-parenchym 



Spermatochnus 



Nemacystus 

 (1 axial thread) 



k 

 7 \^ 



Acrothrichaceae 



Ralfsiaceae 

 (crusts) 



Monopodial 

 branching ^ 



Eudesme 



Myriogloia 



several axia 



threads 



A 



Myrionemataceae reducti 

 (epiphytes) 



on 



Coryno- \Corynophlaea 

 phlaeaceae-^ | 



Leathesia 



reduction 

 Petrospongium 



Elachistaceae 



Cladosiphon 

 (sympodial 

 branching) 



Mesogloia — 

 (1 axial thread) 

 (Chordariaceae) 



->- Caepidium 



