XVII] GENERAL CONCLUSION 345 



podial origin of pinnae laterally upon the phyllopodium has been a secondary 

 modification of dichotomy of the leaf-apex (Chapter v, p. 91). In the latter 

 case the correctness of the view is upheld by the gradual transition to equal 

 dichotomy in the distal branchings of the leaves of many Ferns(303). It is 

 true that in the relations of the leaves to the axis no similar evidence of 

 such a transition reveals the actual origin of leaf and axis. But the view 

 expressed is based on analogy with what is seen in the leaves of Ferns. 

 In point of demonstration the relation of leaf to axis in Ferns is as open 

 a question as that of the pinnae to the phyllopodium of Flowering Plants 

 would have been if no Ferns had survived to give the explanation. 



The simple shoot thus constructed may grow indefinitely at its apex. 

 But frequently it is further amplified by distal branching. This may be 

 either by equal dichotomy, or it may be dichopodial. The former would 

 give a forked shoot as seen in the Frontispiece : the latter would account 

 for the origin of axillary and other buds related to the leaf-base (Chapter iv). 

 Adventitious buds are, however, often formed in addition to these at points 

 not directly related to the apical region. The origin of the whole shoot- 

 system of Ferns may thus be accounted for. On the other hand, the em- 

 bryonic spindle as above defined normally gives rise at points apart from 

 its apex to the haustorium or foot, and to the first root. These are held to 

 be accessory organs formed laterally upon the spindle. The later roots are 

 also accessory, and may be borne on the axis or on the leaf-bases. Hairs 

 and emergences may appear indiscriminately on the free surfaces. 



This hypothesis accounts for the primary origin of all the vegetative parts 

 of the sporophyte. It is stated here in its special application to the Filicales. 

 But the same hypothesis is also applicable — perhaps with some modification 

 as to the mode of origin of the leaves — to other Pteridophytes, and even to 

 vascular plants at large. Those Eusporangiate Ferns which retain the sus- 

 pensor are regarded in this and in other features as relatively primitive in 

 their embryology. They form a natural link between the Class of the Filicales 

 and other great Divisions of the Vegetable Kingdom. The Leptosporangiate 

 Ferns have been shown to be derivative among the Filicales, and they are 

 less clearly in accord with the hypothesis. The facts that their suspensorless 

 embryos were the first to be examined, and that they are so easily obtained 

 for class purposes, have given them an entirely false importance in general 

 morphology, and obscured the recognition of the suspensor as an important 

 vestige. The Leptosporangiatae constitute in fact a line of specialisation 

 peculiar to themselves, which reached its highest development in the Ferns 

 of the present day. Turning to the Lycopodiales their embryology accords 

 with the hypothesis of the primitive spindle, since with the exception of 

 Isoetes they have a suspensor, and endoscopic orientation (see p. 309). But 

 difficulties of embryological comparison certainly exist in such facts as the 



