142 SOIL CONDITIONS AND PLANT GROWTH 



soil that cannot be changed one into the other by any cultivator's 

 artifice. 



Calcareous Soils. The simplest case is presented by soils where 

 the calcium carbonate exceeds about 10 per cent, and dominates every 

 other constituent, becoming the controlling factor in determining the 

 soil properties. The conditions here seem to be extraordinarily well 

 suited to plant and animal life. Bacteria are numerous and active, 

 rapidly oxidising organic matter. Hosts of animals, wireworms, earth- 

 worms and others live in the grass land, and even get into the arable 

 land, honeycombing the soil with their passages, puffing it up or " light- 

 ening " it considerably, and encouraging the multiplication of moles. 

 Rabbits abound in dry places. Vegetation is restricted on thin ex- 

 posed soils, but becomes astonishingly varied where there is sufficient 

 depth of soil and shelter to maintain an adequate water supply. Ash 

 is the characteristic tree in the north and beech in the south of Eng- 

 land, and there is a great profusion of shrubs guelder rose, dogwood, 

 hawthorn, hazel, maple, juniper ; and especially of flowering plants 

 scabious, the bedstraws, vetches, ragwort, figwort. Still more remark- 

 able, perhaps, is the fact that a few plants the so-called calcifuges do 

 not occur. Where the amount of calcium carbonate becomes too high 

 plants tend to become chlorotic ; Chauzit's analyses showed that vines 

 suffered badly when 3 5 per cent, or more was present, but not when 

 the amounts fell to 3 per cent. 1 



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. In a prolonged investigation near Karl- 

 stadt, 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. Brachypodium pinnatum, Kceleria 

 cristata^ and Hieracium pilosella. True chalk plants were found on the 

 adjoining sand, especially when some calcium carbonate was present, al- 

 though 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 



1 See Revue de Viticulture, 1902, xviii., 15, and also Molz, Centr. Bakt. Par., Abt il, 

 1907, xix., 475, 



