V] 



CONCLUSION 



The essential features in the leaf-architecture of the Ferns have been 

 described in general terms in the preceding pages. But many points of 

 importance for comparison have been left over to the detailed description 

 of genera, which will follow in the Second Volume. The leaf-development 

 of Ferns and Pteridosperms stands alone in its complexity and variety among 

 the types seen in Vascular Plants. It is the prototype upon which, by various 

 modifications, the foliar development of Seed-Plants is based. At the same 

 time so many features that are primitive still remain in some of the living 

 Ferns, or are shown in the related fossils, that it is possible to trace with 



Fig. 97. Series of juvenile leaves of Cyathea insignis, illustrating progressive 

 dichopodial development in a relatively primitive type. ( x 4.) 



some degree of certainty the way in which even the most complex leaf- 

 structures have been built up. On the basis of the comparative analysis given 

 above a primitive type of Fern-leaf may be sketched out as a stalked structure 

 with or without basal protective growths ("stipules"), the distal end dicho- 

 tomising as a rule in a single plane tangential to the axis which bears it. 

 Narrow lobes are thus formed, each distinct from its neighbours, and each 

 traversed by a single vascular strand. Living examples are seen in the adult 

 leaves of many of the Hymenophyllaceae, or in Todea siiperba, or in the 

 juvenile leaves of Cyathea (Fig. 97). Later types would show progressive 



