THE ORIGIN AND GROWTH OF PLANT COMMUNITIES 579 



and Castro, 1959). New methods have also been proposed (Schmid, 

 1956; Lems, 1957). 



Any discussion of epharmony poses the question of the relative 

 correspondence of form and function. Any system of life-form classes 

 or categories therefore is based on the premise of an underlying physio- 

 logical likeness. Life-form classes, however, are defined in morphologi- 

 cal terms, and it will always remain to demonstrate whether or not any 

 particular form in general or that particular form in a certain species 

 or individual does indeed serve as an outward sign of a function actu- 

 ally fulfilled. 



Epharmonic schemes therefore have rested on form ( habit, type of 

 leaf) and often on function (nutrition, vegetative response, propaga- 

 tion, periodicity, regeneration ) . Raunkiaer's ( 1907, 1934 ) well-known 

 classification is universally employed and has been used to grade floras 

 and associations. The fourteen stands of Laurentian vegetation re- 

 corded in Table IV show some very important divergences in this re- 

 spect. Thus the forest associations (which all have a heavy tree 

 canopy) vary from 13 per cent (Betuletum populifoHae) to 26.7 per 

 cent of trees (Pg and Pm), whereas, the others have 6.2 per cent or 

 less. The geophytes are also highest in the forest. Cain (1950), Dan- 

 sereau ( 1957a ) , and Cain and Castro ( 1959 ) list many more life-form 

 spectra and discuss their meaning at some length. 



Other gradings have been applied besides Raunkiaer's life forms 

 (see Du Rietz, 1931), some of them much simpler and making fewer 

 assumptions. The types I proposed in 1951 and later modified (1958b) 

 make no functional assumptions whatsoever except those concerning 

 sheer spatial occupancy. Thus erect woody plants are distinguished 

 from climbing or decumbent woody plants, and these in turn from 

 herbs, epiphytes and crusts, and moss-like plants, or bryoids, and they 

 are situated in a vertical scale of seven divisions. Table V shows the 

 distribution of these structure forms among the 14 Laurentian associa- 

 tions. The hanas and epiphytes are absent from these particular stands. 

 The bryoids play an important role in two communities: the Betuletum 

 populifoliae and the Acereto-ulmetum laurentianum. The W/H ratio 

 is lowest in the Poaetum and highest in the Populetum. 



The consistency of the stand also has been the object of analysis, 

 over and above the distinctions just made. Raunkiaer (1934), for in- 

 stance, has proposed a grading of leaf-surface units (see Dansereau, 

 1957a; Cain and Castro, 1959, pp. 275-285). Not only do vegetation 

 types of difiPerent climatic regions diflfer, but contiguous communities 

 belonging to contrasting ecosytems do as well: witness a broadleaf 

 deciduous forest (Aceretum saccharophori ) and a neighboring leather- 

 leaf bog ( Chamaedaphnetum calyculatae ) . 



Other similar gradings involve something more than size-for in- 



