298 



PLANT SOCIOLOGY 



Since a single set of characteristics may be changeable or phenotypic 

 in one systematic group, and unchanging or genotypic in another, it is 

 impossible to separate the sets of characteristics absolutely. It is 

 certain that numerous functionally important morphological characters 

 which are used in Raunkiaer's classification of life forms are firmly 

 fixed by heredity. These permanent genotypic adaptations may have 

 arisen in the past by natural selection, under conditions wholly 

 different from those of today. Their occurrence under definite climatic 

 or edaphic conditions leads to the conclusion that they are in 

 harmony with these conditions but not that they owe their origin to 

 them. 



Life forms cannot, accordingly, be considered as the unequivocal 

 and direct answer of living things to dominant external conditions. 

 Rather they represent a shaping of the more or less fixed phylogenetic 

 basis in response to the particular habitat. 



Life Forms in Plant Geography. — Raunkiaer originally intended his 

 life forms to be used only in the ecological characterization of definite 

 climatic regions, in the description of plant climates. For this purpose 

 he determined the proportion of each life form in the flora of the world 

 as a whole, and, arranging classes in a manner somewhat analogous to 

 the arrangement of the colors of the spectrum, he designated the 

 result a "normal biological spectrum." 



Five of the classes are thought to be most significant and are 

 designated by an appropriate letter here shown following the name. 

 These classes are phanerophytes (F); chamaephytes (Ch); hemi- 

 cryptophytes (H); geophytes (G) (or cryptophytes) ; and therophytes 

 (Th). The biological spectra for the world as a whole (the normal 

 spectrum) and for various typical areas are shown in the following 

 table : 



Table 34. — Biological Spectra According to Raunkiaer 



Region 



Th 



Normal spectrum 



Central Switzerland 



Paris basin 



Switzerland, high Alps. . 



Spitzbergen 



Northern Africa 



Death Valley, California 



Seychelles 



Connecticut 



13 



20 



9 



3.5 

 2 



50 

 42 

 16 

 12 



