EDAPHIC OR SOIL FACTORS: CHEMICAL 187 



Dolomite Vegetatio7i.— Dolomite, a compound of soluble CaCos and 

 rather insoluble MgCOa, supports, in general, the same type of vegeta- 

 tion as compact limestone. The effect of Ca ions is of supreme impor- 

 tance upon dolomite substrata. But whether the exclusively dolomite 

 species (and without doubt there are such) need considerable quantities 

 of magnesium in combination with calcium or are strictly confined to 

 dolomite soils for other reasons cannot now be decided. Perhaps it is 

 only in such places that favorable physical conditions of the soil are 

 found. In future studies of vegetation closer attention will have to be 

 paid to whether or not the soil is dolomitic. 



Numerous dolomite species inhabit the Spanish Sierras, the south- 

 ern Cevennes, and the southern Alps. In some individual cases their 

 limitation to dolomite substrata may be explained as due to their 

 reUct nature. Several of them are rehcts of the Tertiary, with narrowly 

 delimited occurrence such as Armeria juncea, Saxifraga cebennensis, 

 and Arenaria hispida of the C6vennes and Asplenium seelosii and 

 Drdba ladina of the southern and central Alps. 



These are exclusively denizens of the raw dolomitic soils; that is, 

 they are rock or talus plants. As soon as humus is formed upon dolo- 

 mitic rock or gravel, its specific characteristics are lost, and the resultant 

 soil scarcely differs from the adsorptively saturated, mild humus of lime 

 soils. In humid regions the leaching of carbonates sets in upon dolo- 

 mite as upon limestone, and acidophilous plants follow in the train of 

 the progressive acidification of the dolomite soil. This occurrence of 

 silicicolous plants on dolomite substrata was first noticed by Sendtner 

 (1854, p. 330). 



As examples of plant communities of raw dolomitic soils we may 

 enumerate the rock-crevice association of Potentilla caulescens, var. 

 cebennensis and Saxifraga cehennensis and the South Tirolean facies of 

 the Androsace helvetica association; also, the richly colored, unique 

 association of the endemic Armeria juncea, accompanied by Arenaria 

 capitata, Alyssum montanum, var. psammeum, etc., so characteristic 

 of the dolomite vegetation of the southern French Gausses. Certain 

 rock-clinging communities seem also to be pronounced dolomite special- 

 ists. According to Motyka (1926, p. 198), dolomite, hme, and marl are 

 colonized by entirely distinct hchen associations in the Tatra. The 

 hchen vegetation on dolomite is much more sparse and made up of 

 fewer species than that upon lime. Diels's (1914, p. 524) researches in 

 the Dolomites of southern Tirol showed this. Furthermore, the 

 vitality of many species is considerably diminished on dolomite. In 

 part, this may have some connection with the manner of weathering 

 of the rock. But, according to Motyka, the chemical factors are 



