CHAPTER XXI 



THE ANGIOSPERMAE : STEMS 



In the stem of the Angiosperms we have to do with a structure of so protean 

 a nature, so far surpassing the root in the manifold diversities of its form 

 and structure, that we are brought at the very beginning against a fundamental 

 morphological difficulty : How are we to define the stem ? The only all- 

 embracing answer is : " The stem is that organ which bears the leaves." 

 This definition, although correct so far as it goes, reveals the bankruptcy of 

 the old system of morphological categories, for it tells us nothing of the 

 nature of the stem itself, which it describes only in relation to another 

 morphological concept, namely the leaf, and it is based upon function, not 

 upon structure. 



This difficulty has impressed morphologists for more than a hundred 

 years past and has given rise to a variety of theories, which we may group 

 under the general name of phytonism, having the common aim of supplanting 

 the idea of the stem as a distinct morphological entity. Morphologists are 

 still, in fact, pretty sharply divided into those who support this idea and those 

 who do not. 



The old idea formed by the purely descriptive outlook of systematists was 

 that plants consisted of three ultimately distinct categories of organs, each a 

 true unity, namely Rhizome * (root), Caulome (stem) and Phyllome (leaf), 

 each capable of great variation yet each remaining true to its essential nature. 

 This was first challenged by C. F. Wolft' (1759), who maintained that the 

 stem is formed of a bundle of united leaf stalks, prolonged downwards, so 

 that in cutting across an old stem one is really sectioning a mass of leaf traces. 

 This is the prototype of a number of later theories, all based upon the 

 longitudinal segmentation of the stem. Opposed to them are several rival 

 schemes which treat the stem as transversely segmented into a sympodium 

 of units, generally called Anaphytes, each corresponding more or less closely 

 to a single internode with its attached leaf or leaves and their axillary buds. 



We have previously shown (p. 650) that Zimmermann has proposed an 

 analogous view of the elementary morphology of the shoot in which the 

 primitively equivalent segments are called telomes, some fertile, that is to 

 say, spore-producing, and some sterile, evolved from the fertile segments. 

 From these, through the " overtopping " process, all the organs of the higher 

 plant may have been evolved. 



It may be pointed out that most of these theories are purely logical con- 

 structions and that, except in the last case, little or no attempt has been 



* This use of the term Rhizome must not be confused w ith the modern application of the 

 term to an underground stem. 



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