388 Forestry Quarterly 



a more or less distinct life cycle and must face the struggle for 

 existence. In the following pages, in a brief historical way the 

 development of these phases of vegetation will be considered. 



The association of plants is a fundamental law of vegetation 

 and may be defined as the co-habitation of two or more indiznduals 

 or species of plants. Plants may be grouped into association upon 

 various bases. The most important of these are the stratum to 

 which they are attached, the water-content of the soil, and light. 

 Humboldt (20), De Candolle (21), Schouw (22), Meyon (23), 

 Drude (24), and Warming (7) distinguished various kinds of 

 associations based on the stratum to which plants are attached. 

 Schimper (10), in 1898, brought order out of chaos by reducing 

 the number to four, namely: lianas, epiphytes, saprophytes, and 

 parasites, and showing that all other kinds were either identical 

 with these or only slight modifications of them. 



Schouw (22), in 1823, was probably the first to recognize the 

 importance of light associations. He divided plants into darkness 

 plants, shade plants, and light plants. This classification holds 

 good to this day and has been adopted, with small modifications 

 in some cases, by nearly all later investigators, notably Kabsch 

 (25), Warming (7), and Clements (26). 



As early as 1820, De Candolle (21) summarized the character- 

 istics of land and water plants, but he did not evolve a classifica- 

 tion of them. Schouw (22), the noted Danish botanist and plant 

 geographer, was also a pioneer in this connection for he was 

 the first to classify plant associations on the basis of the water- 

 content of the soil. He distinguished: 1. swamp plants; 2. plants 

 which grow in moist meadozvs; and 3. plants that love a dry soil. 

 Meyen (23) added little to Schouw's classification, but Thurmann 

 (27) pointed out that the physical and not the chemical properties 

 of the soil determine water-content. A. de Candolle (28) also 

 recognized this fundamental relation. Warming (7) not only 

 summarized the development of this line of inquiry, but he even 

 went so far as to make water-content of the soil the basis of his 

 entire work. His great contribution to ecology lies in his recog- 

 nition of the fundamental importance of the water-content asso- 

 ciation. He recognized four types of vegetation: hydrophytes, 

 xerophytes, halophytes, and mesophytes. Later (15), Warming 

 modified this classification and made 13 groups also based upon 

 the water-content of the soil, but this new system is considered 



