2 INTRODUCTION chap, i 



for instance, it will be necessary to investigate the following items : 

 the distribution of the species present, their arrangement in the country, 

 the sub-division of Denmark into natural floristic sections, Denmark as 

 a floristic portion of a larger natural district or its floristic affinity with 

 Sweden and Norway, Germany, and other lands, the problems as to 

 when and whence the species immigrated after the glacial epoch, the 

 routes of their migrations and their means of migration, the problem 

 of species left behind (vestigial plants), and the like.^ 



With these interesting and far-reaching results of floristic plant- 

 geography we shall not deal in this work. This subject has been treated 

 by Wahlenberg, Schouw, A. de Candolle, Grisebach, Engler, Drude, 

 and others. 



Oecological plant-geography has entirely different objects in 

 view : 



It teaches us how plants or plant-communities adjust their forms 

 and modes of behaviour to actually operating factors, such as the amounts 

 of available water, heat, light, nutriment, and so forth. 



A casual glance shows that species by no means dispose their individuals 

 uniformly over the whole area in which they occur, but group them 

 into communities of very varied physiognomy. Oecology seeks 



1. To find out which species are commonly associated together 

 upon similar habitats (stations). This easy task merely involves the 

 determination or description of a series of facts. 



2. To sketch the physiognomy of the vegetation and the landscape. 

 This is not a difficult operation. 



3. To answer the questions 



Why each species has its own special habit and habitat, 

 Why the species congregate to form definite communities, 

 Why these have a characteristic physiognomy. 

 This is a far more difficult matter and leads us 



4. To investigate the problems concerning the economy of plants, 

 the demands that they make on their environment, and the means that 

 they employ to utihze the surrounding conditions and to adapt their 

 external and internal structure and general form for that purpose. We 

 thus come to the consideration of the growth-forms of plants. 



CHAPTER II. GROWTH-FORMS 



Every species must be in harmony, as regards both its external 

 and internal construction, with the natural conditions under which 

 it lives ; and when these undergo a change to which it cannot adapt 

 itself, it will be expelled by other species or exterminated. Consequently 

 one of the most weighty matters of oecological plant-geography is to gain 

 an understanding of the epharniony of species. ^ This may be termed 

 its growth-form in contradistinction to its systematic form. It reveals 



^ Warming, 1904. 



^ Vesque (1882 a) defines ' L'epharmonie ' as ' I'etat de la plante adaptee '. 

 Epharmosis, a term also invented by Vesque, on the other hand, denotes the act 

 of adaptation (or the behaviour) of organisms exposed to new conditions. 



