XV] RELATION OF LEAF TO AXIS 315 



be, strict recapitulation cannot be assumed where, as in plants, continued 

 embryology holds sway, with its successive origination of new organs. In 

 plants the primary steps of foundation of the organism are a less important 

 matter than in animals, where the plan of the whole organism is laid down 

 once for all. For plants a line of inductive reasoning is required quite dis- 

 tinct from that which has led to more definite conclusions for animals. 



The facts relating to the suspensor and the initial polarity of the embryo, 

 together with the primary relation of the cotyledon to the apex thus defined, 

 appear on a comparative review of their embryogeny to be the fundamental 

 features for the vascular plants in general, and for the Filicales in particular. 

 The reference of the sporophyte embryo back to a primitive spindle, or fila- 

 mentous row of cells, which has been shown to accord with the facts of 

 embryology, gives a plan of construction of the embryo which is believed 

 to be fundamental and archaic. To those facts which harmonise most readily 

 with that plan the greatest weight is to be accorded, while those features 

 may be held as of less importance for comparative purposes which have 

 had the effect of disguising that original plan. 



In conclusion it may be pointed out that the relation of leaf to axis, as 

 shown in the embryos of Ferns, accords readily with a theory of the ultimate 

 relations of leaf and axis as equivalent branches of an indifferent branch- 

 system, which was possibly dichotomous (Chapter XVii, p. 340). They both 

 originate from the epibasal hemisphere side by side. The one or the other 

 may in concrete cases take precedence in the individual development, a point 

 closely related to the conditions of nutrition. Thus the archaic spindle may 

 have had a power of dichotomous branching at its apex. Whether or not such 

 a primitive sporophyte resembles the actual prototype of the sporophyte of 

 the Filicales, or of the Pteridophyta at large, it is the conclusion to which 

 induction, based upon an organographic study of the adult, combined with 

 the facts of embryology, and the evidence of palaeontology, appears naturally 

 to lead. 



Postscript 



Since this Chapter was written still another view as to the constitution 

 of the leafy shoot as seen in Ferns has come into prominence. The theory of 

 the "phyllorhize" has been propounded by Chauveaud (265), and expounded 

 by Becquerel(266). It claims to be based upon the ontogenetic method, and 

 the central idea is that of a body designated the " phyllorhize," consisting 

 of an upward-directed leaf and a downward-directed root, connected by a 

 middle-region or stalk (caule). It is stated that in a young Fern composed 

 of one or more of such units there is at first no stem (tige). This comes 

 only into existence when a fusion of units has taken place. It then origin- 

 ates laterally upon the " phyllorhize," as a bud which transforms itself 



