THE WOODY DICOTYLEDONS 385 



would be put in a higher taxonomic position than Ranunculus, 

 because its reproductive structures present a condition of cohesion 

 not found in the flower of the buttercup. The suggestion that 

 Casuarina owes its anatomical organization to its xerophytic 

 habit must be definitely rejected because of the extremely general- 

 ized type presented by the organization of its woody structures. 

 In the single genus under consideration all the types of rays found 

 in dicotyledons, as has been shown in an earlier chapter, are 

 presented in the different species. Since all the species are equally 

 xerophytic, it is quite impossible to connect any type of radial 

 parenchymatous organization with the xerophilous habit. Physio- 

 logical or ecological explanations of anatomical facts are always 

 to be welcomed when they have any logical probability, but when 

 they fail in this respect they only obscure the evolutionary situa- 

 tion. The general anatomical evidence in the case of the interest- 

 ing genus Casuarina seems, in the present state of our knowledge 

 at any rate, entirely to justify the primitive position assigned 

 to it in the great systematic work of Engler and Prantl, in which 

 it is placed at the very base of the dicotyledons. 



If on anatomical and other grounds Casuarina must be regarded 

 as a primitive representative of the dicotyledonous angiosperms, 

 it is equally clear on the same evidence that with it must be joined 

 the Betulaceae and Fagaceae and in all probability the Ericaceae. 

 The usual fusion of parts in the flowers of the groups enumerated 

 cannot apparently, in view of the overwhelming anatomical 

 evidence for their primitive position, be regarded as a very im- 

 portant systematic criterion. Wind pollination and the general 

 absence of herbaceous forms further supply striking features of 

 conformity to the conditions found in the higher gymnosperms 

 from which it is very likely the dicotyledons have taken their 

 origin. 



Another assemblage of forms which has been pushed into the 

 foreground, particularly in recent years, as the primitive repre- 

 sentatives of the dicotyledonous angiosperms are the Ranales. 

 Without discussing whether the families included under this 

 general heading all properly belong here, we may point out that 

 on anatomical grounds the claims of that group to affinity with 



