16 SPHENOPHYLLALES [CH. XII 



homogeneous whole. There is much that is attractive in the 

 view recently propounded by Mr Tansley that a leaf is not an 

 appendicular organ differing ab initio from the axis on which it 

 is borne, but that it is in phylogenetic origin a " branch-system 

 of a primitive undifferentiated sporangium-bearing thallus^" 

 Admitting the probability that this view is correct, our faith 

 in the importance of discussions on the morphological nature of 

 sporangiophores is shaken, and we realise the possibility that 

 our zeal for formality and classification may lead to results 

 inconsistent with an evolutionary standpoint^. 



1 Tansley (08) p. 26, who refers to similar views held by Potoni^ and by 

 Hallier. 



2 On the morphology of Sporangiophores, see also Benson (08^) and 

 Scott, D. H. (09) p. 623. 



