76 PLANT MORPHOLOGY 



from it. The primitive cortex from which the appendages sprang 

 may remain a continuous, undifferentiated band, as it actually 

 does appear in the vast majority of leafy sporophytes; or it may 

 in certain cases be more or less clearly marked off into regions sur- 

 rounding the insertion of the individual leaves. But in the fact that 

 these special cases exist I see no sufficient foundation for the view 

 that each leaf is, in shoots at large, connected with a definite area of 

 extended leaf-base: and still less for the theory that in vascular 

 plants the cortex originated from such coalescent leaf-bases. Our 

 theory of the strobilus would indeed presuppose that close relation 

 of cortex and appendage, and absence of limit between them, which 

 is so common a feature in vascular plants: and furthermore, it will 

 readily cover the facts where the cortex is delimited into definite 

 areas round the leaf-bases: but it does not recognize any necessity 

 for generalizing from such cases of special delimitation, that the 

 cortex is foliar in its origin, in shoots of vascular plants at large. 

 It would be more ready to suggest the converse, viz., that the leaves 

 were cortical in their origin, as indeed they are in the ontogeny. 



Discussions such as these on phytonic theory, or theory of corti- 

 cation, are liable to develop into mere scholastic contests. They 

 originated in the present case in the use of terms in an unprecise 

 sense, and the subsequent attempt to attain precision. Both these 

 theories have proceeded from the assumption that the "leaf" is 

 an abstract entity, distinct from the stem. Difficulties arise when 

 the attempt is made to carry out that distinction sharply in practice, 

 for this is nothing less than the attempt to define precisely things 

 which in point of fact appear neither uniform nor precise in nature. 

 The strict definition of terms used in morphological science is doubt- 

 less in itself a desirable thing; but it must be so conducted as to 

 harmonize with the facts of individual development, while at the 

 same time it must not violate evolutionary probability. As a matter 

 of fact, neither in the mature state, nor in the ontogenetic or phy- 

 logenetic development of the leaf, does the structure suggest its 

 sharp delimitation from the axis as a general feature in the shoots 

 of ordinary vascular plants. 



My present position with regard to the phytonic theories and 

 the theory of cortication is frankly destructive: for, in the first 

 place, if the evidence from the gametophyte generation be discounted, 

 the facts of segmentation in the sporophyte are of the slenderest: 

 further, I do not think that morphological insight will be advanced 

 by attempts to define precisely the limits of the parts of the vascu- 

 lar shoot; it seems more in accordance with nature to accept for 

 vascular plants the view of Braun and of Sachs, that the shoot is 

 the original unit. What is first urgently required, in order to decide 

 such questions, is the correct recognition of the phyletic lines which 



