28 



PLANT SOCTOLOGY 



many portions as complete and mutually exclusive association samples 

 (containing the normal combination of species) can be made from it. 

 For diagnostic purposes and for many ecological and syngenetical 

 studies it is necessary to investigate the largest possible portions of the 

 uniform area. To give just one example: The Seslerieto-Semper- 

 viretum of the Central Alps originates on alkaline or neutral soils, but 

 the accumulation of humus, combined with leaching, transforms these 

 to a very acid condition. Unmistakable indicators of this acidifying 



Fig. 10. — An open terraced stand of the Seslerieto-Semperviretum, var. tatricum upon 

 steep limestone rubble in the Tatra, at 1,830 m. {Photo by Zlatnik.) 



process are the acidophilous companion species which come in and 

 gradually increase during the course of the acidification (Braun- 

 Blanquet and Jenny, 1926). This transformation of vegetation can 

 be recognized and understood only when the uniform stand is studied 

 floristically in every part. Portions of 10, 20, or 50 sq. m. do not 

 suffice to include, especially in the earlier stages of development, the 

 very sparsely scattered acidophilous indicators, much less to discover 

 their sociologic significance {cf. Alechin, 1925). The larger the num- 

 ber of species and the more mixed the community the less satisfactory 

 is a limited number of small and arbitrarily bounded samples (meter 

 quadrats). 



To give the data accuracy and completeness, the following proce- 

 dure is suggested: Begin with the record of a small sample plot (in 



