. WITHIN THE GfCNUS DENUIIOXEPHTHYA. of) 



It is quite conceivable bhat species which have attained individu- 

 ality and fixity in the course of isolation and inbi'eeding may be 

 brought into contiguity by subsequent spreading or removnl of 

 barriers. In such a case, analogy points to the likelihood of 

 numerous new patterns arising by permutations and combinations 

 of the previously segregated species. This hypothesis is certainly 

 suggested by the fact that two species may agree in anthocodial 

 armature and yet differ in mode of branching, or may agree in 

 having a foliaceous collar and yet differ in the nature of the 

 supporting bundle. In short, in the distinctions between species 

 there is a distinct suggestion of the shuffling of unit characters. 



III. There seems to be a third possible interpretation — namely, 

 a mutation of species apart from any hybridizing influence. It 

 may be that certain widespread and strongly established species 

 such as D. giganiea, D. ehrenbergi, and D. hrevirama have been 

 the stocks from which mutations have been thrown off after the 

 fashion of (Enothera lamarckiana. 



An indirect argument in favour of this interpretation may 

 perhaps be found in the possibilit}^ of discriminating similar 

 radiations of evolution within the three great groups : Glomerates, 

 Divaricates, a,nd Umbellates. A more direct argument may be 

 found in the variability of certain species such as D. gigantea, to 

 which reference has already been made. As Kiikenthal remarks, 

 " Aus diesen Beschreibungen geht hervor, dass B. gigantea eine 

 in ihrem Aufbau sehr variable Art ist." (' Revision,' p. 553.) 



§ 4. Kiikenthal has divided this difficult genus into the three 

 main groups: (I.) Glomeratse ; (II.) Divaricatfe ; (III.) Umbellatse, 

 giving precision to similar suggestions by previous workers such 

 as Holm. 



I. The Glomeratse are characterized by : — 



{a) the comparatively slight branching of the polyparium ; 



(6) the grouping of numerous bundles of polyps into roundish 



bunches Avhich make the surface of the polyparium 



entirely irregular. 



There is a marked definiteness about the Glomerate division 

 which suggests " naturalness," and makes it easy to refer a 

 species to the group. Text-fig. 1 is a diagrammatic illustration 

 of what is meant by the Glomerate habit of growth. 



II. The Divaricatse are characterized by : — 



(a) the profuse branching of the polyparium ; 



(6) the length and slenderness of the twigs ; 



(c) the divergent separateness of the polyp bundles ; 



{d) the absence of anything that can be called bunches of the 



Glomerate type or umbels of the Umbellate type. 

 It should be noted that a Divaricate polyparium may have a 

 continuous contour like that of a well-pruned tree (see diagram). 



3* 



