220 



PLANT SOCIOLOGY 



Table 25. — Soil Temperatures (3 to 5 Cm, Deep) in Weathered Rubble 



WITHOUT Humus 

 (After Henne) 



Kind of rock 



Soil color 



Mean, 



degrees 



centigrade 



Mean maxima 



(1 p.m.), degrees 



centigrade 



Slate 



Verrucano 



Gneiss 



Jurassic limestone 



Cretaceous limestone . 

 Clay soil 



Black 



Red 



Yellowish gray 



YeUow 



Gray 



16.8 

 16.8 

 16.2 

 15.9 

 15.4 

 15.4 



20.4 

 20.3 

 19.5 

 18.2 

 17.5 

 17.5 



The mean temperature of the air at the same time was 14.2°C.; the 

 mean maximum, 15.6°C. The soil temperature during the seven 

 months of the experiment was considerably higher than the simulta- 

 neous air temperature; the temperature of black soils was considerably- 

 higher than that of soils of other colors. This circumstance makes 

 thinly vegetated basalt, phonolite, serpentine, and dark-colored dry, 

 porous soils in general especially well suited for thermophilous southern 

 plant communities. Among such soils are the volcanic soils of the 

 Hegau, of the Kaiserstuhl, of the Auvergne ; the serpentine soils of the 

 Mur valley in Styria and the basalt soils of southern France. The flora 

 and vegetation of the basaltic soils of Roquehaute near Agde, France, 

 are famous throughout Europe. There in a limited area are found a 

 whole group of liverworts, mosses, and flowering plants, whose main 

 distribution is in northern Africa. The peculiar Isoetes setacea associa- 

 tion, with Marsilia puhescens, Pilularia minuta, and Peplis erecta, is 

 nowhere else in all France so richly developed and so abundant as it is 

 around the black pools of Roquehaute, which in the summer for weeks 

 at a time are decidedly hot. Ramann (1911, p. 395) has emphatically 

 stated the important influence of soil structure upon soil temperature. 

 In Wirkung treten die hohe Wasserkapazitat, Wdrmebindung infolge 

 Verdunstung, Anderungen der Temperatur tieferer SchicUen heim 

 Eindringen von Wasser und der Einfluss von Oberfldchenwasser auf die 

 Bodentemperatur. Thus the effect of water is very considerable. The 

 so-called "cold soils"— humus and clay — are very retentive of water. 

 G. Kraus (1911, pp. 120-123) has shown by numerous measurements 

 the differences between the temperature of wet and dry soils. Unfor- 

 tunately he did not attempt to discover any relation of this to the 

 vegetation. 



