Chap, ii The Theory of Metamorphosis 79 



leaf-bearing axes are not to be found. It is therefore 

 a matter of convenience where the boundary-line is drawn ' ; 

 and again, ' The expressions thallome, caulome, phyllome, 

 trichome, root, designate, as has been said, several ideas V 



The development of the idea of metamorphosis, taken 

 in the sense in which Sachs used it, itself proceeded on the 

 lines of adaptation. Its most eminent exponent was Goebel, 

 who may in many respects be looked upon as Sachs' 

 successor. It was, as interpreted by him, fundamentally 

 morphological rather than physiological, though it recog- 

 nized the direct influence of the environment as a factor 

 in determining form. Writing in 1895, Goebel interpreted 

 metamorphosis as implying the perception that the variety 

 in external form exhibited by plants is to be traced back 

 to the diverse modifications of a very few fundamental 

 types. He said that its study is very closely bound up 

 with that of adaptation, and it might almost be asserted 

 that a metamorphosed structure owes its existence to an 

 adaptive modification of a relatively primitive type form. 



Goebel admitted that in certain cases it is not possible 

 to differentiate the members of the plant definitely into 

 leaf — stem — root, but he opposed the idea that this negatives 

 the metamorphosis of one of these into another or of 

 metamorphosis within the limits of each category. He set 

 out with fairness the impossibility of drawing a definite 

 line of demarcation in all cases between leaf and stem, 

 instancing the various shoot-like members of certain species 

 of Uiricularia, which he claimed to have the morphological 

 value of leaves. He held, however, that though such a 

 definite separation of the two, of universal application, 

 cannot be found, yet such becomes practicable when we 

 limit our consideration to single groups of tolerably closely 

 allied forms, and that this is sufficient for the purpose of 

 the theory of metamorphosis. The leaf and shoot rudi- 



1 The italics are the Author's. 



