288 PLANT SOCIOLOGY 



reproduction. Warming's own system of life forms, however, has 

 found httle acceptance, perhaps just because of its variety and its 

 lack of a coordinating principle. Nevertheless, from the ideas of 

 Warming has developed the system of life forms by Raunkiaer, which 

 is today generally accepted in its most significant features. 



Raunkiaer's System. — Based upon sound morphological and 

 biological principles, Raunkiaer's system is marked by simplicity, 

 clarity, and compactness. The principle of classification is simple. 

 No attempt is made to take account of all the infinite variety of 

 ecological adjustments. Instead, Raunkiaer chooses for his basis of 

 classiilcation a single very important feature, namely, the adjustment 

 of plants to the unfavorable season. It is this which gives the system 

 its clarity and completeness. Plants with similar adjustments are 

 first classified in five main types (life-form classes). Within each 

 class a number of subtypes or life-form groups are distinguished. 



The position of a plant in this system is determined by the location 

 and protection of the perennating organs during the unfavorable 

 season, that is, during the cold winter or the dry, hot summer. On this 

 basis Raunkiaer distinguished: phanerophytes, chamaephytes, hemi- 

 cryptophytes, cryptophytes, and therophytes. The cryptogams are 

 not included in this system. Later, Raunkiaer raised the number of 

 life-form classes by the segregation of stem succulents, epiphytes, 

 helophytes, and hydrophytes. Allorge, Gams, E. Frey, Hayek, 

 Jenny-Lips, Linkola, W. Koch, Ostenfeld, Vahl, Braun-Blanquet, 

 and others have made changes in the designation and limitation of 

 some of the types. ^ 



The value of Raunkiaer's concept, however, seems to be a relative 

 one. In investigations of the vegetation of the high Alps Braun- 

 Blanquet (1913, p. 38) reached the conclusion that for many of the 

 alpine species their success in life depends not on their adaptation to 

 the rigorous season (winter) but rather to their adjustment to the 

 very short, cool summer. He says: 



The better a species can adjust itself to the short vegetative season, the 

 more rapidly it completes its life cycle the more completely is it suited to 

 live and spread in the high Alps. Probably the determining factor for the 

 northern extension of the range of many arctic plants is the preparation of new 

 buds in the fall, or under the snow covering, and the consequent rapid resump- 

 tion of vital activities in the spring with early fruit formation during the 

 favorable season. 



* Du Rietz (1931) has given a careful analj'sis of all the literature relating to 

 the various classifications of life forms. This includes an extensive bibliography 

 and suggestions for a new classification with many new subdivisions. 



