IV] GENERAL CONCLUSION 79 



been held to indicate an adventitious origin, though their constancy and 

 similarity of position suggest comparison with certain buds of the leaf-base 

 which result from dichotomy. Each such case presents its own problem, 

 and it is only by the solution of such separate problems that the line can be 

 drawn between those innovations which are referable to distal dichotomy 

 and those which are really adventitious. Both methods of amplification of 

 the vegetative system certainly exist in Ferns, but recent investigations show 

 that the former may account for a larger proportion of the buds observed 

 than had been anticipated by earlier writers. Consequently the position 

 comes to be substantially that stated by Hofmeister, viz. that in Ferns the 

 branching may be referred either to dichotomy, with equal or tmequal develop- 

 ment of the resulting shanks: or to the formation of adventitious buds. But 

 the line of distinction betzveen these is not always clearly perceptible. 



The conclusion thus reached by comparative analysis of the shoot- 

 system of the Filicales has important bearings upon the morphology of the 

 Higher Plants on the one hand, and on the other upon that of the primitive 

 sporophyte. In the light of what is seen in Ferns the prevalent axillary 

 position of the buds in Flowering Plants is no longer a thing apart. The 

 sharp distinction betu^een the monopodial and the dichotomous branching 

 is obliterated by the recognition of the gentle intermediate steps that exist 

 between them: and the whole construction of the shoot-system of Phane- 

 rogams takes its natural place as a final derivative from a dichopodial state, 

 already foreshadowed in the shoot-system of the Filicales and Pteridosperms. 

 On the other hand, the recognition of the various branchings seen in Ferns 

 as derivatives of dichotomy will suggest the possibilities that lay before a 

 primitive sporophyte having a dichotomous system still undifferentiated: a 

 state which is actually seen in the Psilophytales(62). By its sympodial 

 development leading to strong inequality, and even to positive difference 

 of form of the two shanks, the possibility of the evolution of a shoot with 

 distinct axis and appendicular branches ranking as leaves is clearly present 

 (see Chapter XVll). 



As regards the phyletic treatment of the Filicales themselves, the equal 

 dichotomy being held as the original type of branching, those shoots which 

 dichotomise equally will be held as primitive in that feature, and any de- 

 parture from equality will be held as derivative. Those Ferns in which the 

 anatomical structure of the petiole most nearly approaches that of the axis, 

 as it does in the early fossil Botryopteris cylindrica, and in Stromatopteris 

 and the Hymenophyllaceae among living Ferns, will be held to be relatively 

 primitive in respect of that feature in their morphology. 



