THE SOIL IN RELATION TO PLANT GROWTH 305 



amount of nitrogen, potash, and phosphoric acid in the various 

 crops was apparently unaffected by the carbonate, but the iron 

 was notably depressed. 



The reason for these special features is not clear, but is 

 probably not to be found in any one factor. The plants do 

 not require such high amounts of calcium carbonate, because 

 they will wander on to an adjacent loam ; even the absence of 

 the calcifuges cannot always be attributed to a supposed toxic 

 effect of calcium carbonate, because in other regions, or in pot 

 experiments, some at any rate of them may be found growing 

 in its presence. The lupin affords an example. It is much 

 grown in Germany and is supposed to suffer in presence of 

 chalk (Kalkempfindlichkeit) : Hiltner proposed to use ferrous 

 sulphate to counteract this trouble. But in experimental 

 plots Pfeiffer and Blanck l obtained even better growth in 

 presence of chalk than in its absence ; possibly the beneficial 

 effect was on the nodule organism rather than on the plant. 

 Rhododendrons and azaleas in this country are said to be 

 intolerant even of traces of chalk, for which reason hard 

 water is not used for them ; this case deserves further in- 

 vestigation. In a prolonged investigation near Karlstadt 

 Kraus (155) found no plant occurring exclusively on soils 

 with even approximately equal content of calcium carbonate, 

 although some preferred more, e.g. Festuca glauca^ Teucrium 

 montanum, and Melica ciliata, while others preferred less, e.g. 

 Brachypodiurn pinnatum, Kceleria cristata, and Hieracium 

 pilosella. True chalk plants were found on the adjoining 

 sand, especially when some calcium carbonate was present, 

 although the true sand plants did not wander on to the chalk. 

 In such cases of displacement or " heterotopy " it was shown 

 that the general physical conditions of the two locations were 

 similar in spite of their wide difference in chemical composi- 

 tion. Kraus, therefore, argues that the true chalk plants 

 inhabit chalk soils not because they need much calcium car- 

 bonate, but because they find there the general physical and 

 chemical conditions they require. Dr. Salisbury's view (242) 

 1 Mitt. Land* Inst., Breslau, 1914, 7. 

 20 



