292 EVOLUTIONARY BEARINGS OF THE RESULTS [CH. 



which is presented by the phyletic facts relating to Ferns, when traced from 

 early geological times to the present. 



There is thus reason to believe in some secular establishment in the Ferns 

 of new inherited features that are adaptive, from adjustments originally 

 ontogenetic. The effect of this should be to relax the statement of a general 

 and rigid negative. Any student of Nature who is duly impressed by the 

 infinite possibilities of life will look with distrust on a general dictum that 

 imposes a limit upon them. The utmost that can legitimately be said in 

 opposition is, that the positive evidence of inheritance of adaptive adjust- 

 ments of the individual has hitherto been insufficient to afford general proof: 

 and that is very different from a negation. On the other hand, to most 

 botanists a sharp antithesis between somatic cells and germ-cells, in respect 

 of their receptivity for the impress of characters, seems inherently improbable 

 for Plants. Comparative study of such primitive Plants as the Algae suggests 

 that the zoospores and gametes were originally alike, the latter being probably 

 specialised forms of zoospores: that is, of somatic cells. Even in the Higher 

 Plants the distinction between somatic and germ-cells cannot be drawn by 

 the most exact microscopic analysis till a late stage of development has been 

 reached ; while it is a common experience for active somiatic cells to be 

 aroused to regeneration, and so ultimately they may produce germ-cells. 

 The commonness of fluctuating variations, and the extreme sensitiveness 

 seen in the adjustment of developing plants to their environment, prove 

 how readily the somatic cell is influenced. But the difficulty in obtaining 

 experimental evidence of the inheritance of such adjustments shows how 

 resistant the germ-cells are to fresh impressions. In this, however, there is 

 no justification for holding the difference as absolute. The facts derived from 

 the comparative study of Ferns certainly indicate that it is not. They favour 

 the acceptance of some form of Mnemic Theory as a working hypothesis for 

 Plants, until a final decision shall have been obtained. 



It should, however, be realised that this discussion touches only one facet 

 of the infinitely varied problem of Evolution, though that facet is of prime 

 importance. The complexity of the whole problem appears to show that no 

 single solution of it is probable: but rather that the mechanism of Evolution 

 has been, and is, as complex as the consequences are diverse. Nevertheless 

 if we recognise the secular origin of hereditary changes carried out with wide 

 homoplasy; and consider its cumulative effect in form and structure, this 

 would afford some elucidation of parallel development in respect of indi- 

 vidual criteria, in phyla distinct from one another since early Palaeozoic time. 

 Such detailed steps would bear their own value in contributing to more 

 general conclusions. 



There lies beyond this still the obscure question of causality. Does the 

 initiative to develop an adaptive feature spring from within the organism, 



