ON METAMORPHOSIS IN PLANTS. 115 



bearing structures probably already existed as such (phylo- 

 genetically speaking-) long before the vegetative structure 

 on which they are now borne had reached its present 

 decree of differentiation. Later on it will be made clear 

 how it became customary to disregard the function of any 

 plant-member, and to consider its position and mode of 

 origin as alone of essential importance ; for the present it 

 will suffice to state that most investigators are agreed that 

 the vegetative and the reproductive organs belong to dis- 



tinct categories. 



As regards the vegetative organs, it is admittedly 

 difficult to fix upon any universally valid mark by which 

 it would be possible to definitely differentiate, e.g., all stems 

 from leaves, or even stems from roots. But this does 

 commonly become possible when we limit our consideration 

 to single groups of tolerably closely allied forms, and this is 

 sufficient for the purpose of the metamorphosis question. 

 Nevertheless it must be admitted that families of plants 

 exist in which the limits, for example, between stem and 

 leaf (Caulome and Phyllome) become completely obliterated. 

 An instance of this is seen in the plants composing the 

 natural order Lentibularieae, and especially in the species of 

 Utricularia. The floating, free-growing lateral shoots which 

 branch and bear the inflorescences of our common Utri- 

 cularias, as regards their " morphological value," are leaves ; 

 and the same is true of the creeping, branched shoots of the 

 terrestrial species. But these "leaves" also possess other 

 characters usually attributed to stems. The line of de- 

 marcation between stem and leaf here completely dis- 

 appears. In the more primitive species of this genus the 

 leaves, however, may still perhaps be recognised by their 

 apical growth. Similar remarkable cases of transformation 

 are to be met with in roots, and to these we shall revert 

 later on. 



The question which immediately meets us is this : What 

 significance are we really to attach to metamorphosis ? 

 Many answers have been given to this much-discussed 

 question, and many have written on the subject without 

 having, in the first instance, really formed any clear ideas 



9 



