THE MORPHOLOGICAL COMPOSITION OF PLANTS. 47 



ology : its History and Present Condition," * whence I have 

 already quoted, Dr. Masters indicates sundry of the grounds 

 for thinking that there is no impassable demarcation between 

 leaf and stem. Among other difficulties which meet us if we 

 assume that the distinction is absolute, one is implied by this 

 question : — " What shall we say to cases such as those 

 afforded by the leaves of Guarea and Tricliilia, where the 

 leaves after a time assume the condition of branches and de- 

 velop young leaflets from their free extremities, a process less 

 perfectly seen in some of the pinnate-leaved kinds of Berberis 

 or Mahonia, to be found in almost every shrubbery ? " 



A class of facts on which it will be desirable for us here to 

 dwell a moment, before proceeding to deal with the matter 

 deductively, is presented by the Cactacece. In this remark- 

 able group of plants, deviating in such varied ways from the 

 ordinary phaenogamic type, we find many highly instructive 

 modifications of form and structure. By contemplating the 

 changes here displayed within the limits of a single order, 

 we shall greatly widen our conception of the possibilities of 

 metamorphosis in the vegetal kingdom, taken as a whole. 

 Two different, but similarly-significant, truths are illustrated. 

 First, we are shown how, of these two components of a 

 flowering plant, commonly regarded as primordially distin- 

 guished, one may assume, throughout numerous species, the 

 functions, and to a great degree the appearance, of the other. 

 Second, we are shown how, in the same individual, there 

 may occur a re-metamorphosis: the usurped function and 

 appearance being maintained in one part of the plant, while 

 in another part there is a return to the ordinary appearance 

 and function. We will consider these two truths sepa- 

 rately. Some of the Euphorbiacece, which simulate 

 Cactuses, show us the stages through which such abnormal 

 structures are arrived at. In Euphorbia splendens, the lateral 

 axes are considerably swollen at their distal ends, so as often 

 to be club-shaped : still, however, being covered with bark 



* See British and Foreign Medico- Chirurgical Review for January, 1862. 



