68 PLANT SOCIOLOGY 



tion may be predicted with a high degree of probability, as far as this is 

 possible from historico-geographie evidence. 



In tracing out the rare but floristically rich association of Helian- 

 themum hirtum, Onohrychis caput-galli, and Barhula gracilis and also in 

 bounding the area of the Xerobrometum in southern Germany and 

 northern Switzerland, the records of localities of the characteristic 

 species served as unfailing guides (Braun-Blanquet, 1925, p. 138). 

 To find a well-developed Piceetum in the alpine valleys, it is necessary 

 only to seek out a place from which Listera cordaia, Pirola uniflora, and 

 Lycopodium annotinum, the characteristic species of the association, 

 have been recorded. 



On the other hand, surprising discoveries often result from careful 

 study of fidelity, such as the presence of Sihhaldia procumbens in the 

 Tatra (Pawlowski) or of Polygonatum officinale in the oak scrub of the 

 Gelting peninsula (W. Christiansen). 



The use of characteristic species for classification of communities 

 will be discussed in another connection. 



Characteristic Combinations of Species. — The characteristic species 

 together with those of the highest degrees of constancy, i.e., species 

 present in at least 60 per cent of the stands compose the complete 

 combination of species characteristic of the community. As a rule, a 

 single example of an association will not include all of the characteristic 

 species nor all of the species of high constancy. From the association 

 tables may be deduced which of these species, on the average, will occur 

 in a well-developed example. Thus average characteristic and more or 

 less constant species taken together compose the normal characteristic 

 combination of species. The larger the ratio of the number of con- 

 stant species to the total number of species the more uniform is the 

 association; the larger the ratio of characteristic species the more 

 sharply the association is characterized floristically or ecologically. 

 Those associations are best established which fulfill both conditions. 



Procedure Recommended for Making Records of Vegetation and Constructing 

 Association Tables. — The following example is taken from a vegetation record of 

 a pure beech wood between Kriizenbiihl and Hohenkrahen, Hegau, South Ger- 

 many — date: June 8, 1927. This high forest lies on a non-calcareous morainal 

 terrace (high terrace gravel), sloping eastward at 580 m., and is utiUzed by selective 

 cutting. On this account there are two facies of undergrowth. The facies domi- 

 nated by Carex pilosa in the more open places has a light ratio (Lichtgenuss) of 

 H to }4- The Asperula odorata facies in the denser places has a light ratio of 

 only J^2- In the Asperula facies tree tops eight-tenths closed, cover 4. On 500 

 sq. m. there is an average of eight beeches, sixty to eighty years, 15 to 20 m. tall, 

 slender, branches beginning at 8 to 10 m. Epiphytic societies fully developed, not 

 examined. In Asperula facies a 100-sq. m. homogeneous sample is na^rked off 

 and investigated: 



