THE SPERMATOPHYTA : GENERAL INTRODUCTION 653 



fundamental unity between the upward and downward phases of the 

 main axis. 



Evolutionary morphology thus reduces the cormophyte body to a differ- 

 entiated system of axes and does away with the presumed fundamental 

 character of the division into stem, root and leaf. 



Phytonic Theories of the Shoot 



If the leaves, in whatever form they appear, are no more than the 

 elaborated segments of the axis, they may easily be conceived as replacing 

 other axial segments or as combining to form compound axes of a higher 

 order. In the various Phytonic theories this is envisaged as happening. 

 The different theories called by this name agree in one essential respect, 

 that they all regard the phyllomes as taking some part in the building of the 

 axes, at least in Spermatophyta. As they are based upon the morphology of 

 higher plants they should be limited to them in their application. Thus 

 restricted many objections to phytonism disappear. 



Lotsy summarizes the existing morphological theories of the shoot system 

 as follows : — 



1. The stem and leaves are distinct entities, the leaves being appendages 



of the stem. This was the classic view and is that upheld by 

 Bower's strobilus theory. 



2. The shoot is composed of segments, each consisting of a portion of 



the stem and the leaf belonging to it. This was the original 

 " phyton " theory of Gaudichaud (1841), who regarded the stem 

 as being longitudinally segmented into phytons ; another form 

 of the theory was suggested by Goethe (1817) and later was adopted 

 by Celakovsky (1901), whose " short segments " or anaphytes 

 were transverse units, corresponding to single internodes, with 

 the upper node and leaf in each case. 



3. The stem has no separate existence and is composed of the expanded 



and fused bases of the leaves. This view is associated with Delpino 

 (18S3). He described the stem as a pseudaxis or phyllopodium 

 and the unit components as merithalli. 



4. The shoot consists entirely of axial structures, the lateral branches 



being metamorphosed into leaves. This is essentiallv the telomc 

 theory. Under this heading may also be grouped the Pericaulome 

 theory of Potonie (1903), who first proposed the idea of shoot 

 evolution described on p. 647 as " overtopping." His theory goes 

 further, however, in suggesting that the stem in the vascular plants 

 is a compound structure or pericaulome consisting of a primitive 

 axis which has been surrounded by a cortex consisting of the 

 extended bases of the side shoots, now metamorphosed into leaves. 



5. The stem is a compound structure consisting of a central axial portion 



which has been corticated by the extension of the leaf bases around 



