THE ENVIRONMENT 



303 



tions. Because climate is all important in the control 

 of plant distribution, these schemes can be related 

 to climate. One of the earliest and still very useful 

 schemes is Raunkiaer's method of classifying plants 

 by their life fonn and of compiling the life forms of a 

 locale's plants into a biological spectrum. A spectrum is 

 a percentage analysis of an area's plants classified ac- 

 cording to the position of their regenerating parts. 

 Regenerating parts (usually buds) are those portions 

 of plants from which new growth originates after the 

 dormant period. The dormant period exhibits the 

 death and loss of certain aerial parts of many species. 

 Life form spectra have little direct bearing upon 

 the taxonomy and phylogeny of plants. For example, 

 certain mosses, ferns, and flowering plants are within 

 a single life form class, and individual higher taxa are 

 scattered throughout many classes. This should be 

 expected, because plants within any major taxon usu- 

 ally are adapted to unlike environments. Broad 

 ecological occurrence is manifested especially by the 

 flowering plants. 



On the basis of the position of the regenerating 

 parts, five major life form classes often are used (Fig- 

 ure 17.3). (Neither the full number of categories, nor 

 the subunits originally proposed by Raunkiaer are 

 usually used at the present time.) Phanaerophyles [PH) 

 are trees and shrubs; chamaephyles (CH) are aerial 

 plants, generally herbs and smaller shrubs; hemicrypto- 

 phyles (//) die back to and regenerate from the sur- 

 face of the ground; geophyles (G) have their regenerat- 

 ing structures below ground level; and Iherophyles (Th) 

 are annuals. 



Raunkiaer formulated the concept of the biological 

 spectrum to show the over-all adaptations of plants to 

 local conditions. He determined the percentage oc- 

 currence of each life form for particular areas of the 

 world and the world average for plants in general. 

 His and other samplings of the flora of certain parts 

 of the world indicate the prevalence of phanerophytes 

 in the moist warm tropics, of hemicryptophytes in 

 moist temperate areas, and of therophytes in dry re- 

 gions. Moreover, Raunkiaer concluded that local 



seeds 



^ 



r 



\ - ,\>Ur/-T;-/ 



Phanerophyte 



Chamaephyte Hemicryptophyte Geophyte Therophyte 



Figure 17.3 Raunkaier's plant life forms. Examples of the major life forms and tfieir appearance 

 during unfavorable (above) and fovoroble (below) seasons. 



