94 THE FACTORS [Part I 



Besides its action in producing special varieties, calamine soil is also distinguished 

 from that of other neighbouring localities by the assemblage of plants composing 

 its flora. Viola lutea is completely absent from the Rhine country, and is first seen 

 near Liege. Alsine verna, also common on calamine soil near Aix, is still further 

 separated from its other localities. Armeria vulgaris is near Aix confined to 

 calamine soils, and Silene inflata, var. glaberrima, is surprisingly abundant and 

 luxuriant in places that are richest in zinc. 



Plants of calamine soils contain zinc in all their parts; Risse found 13-12 % of zinc 

 oxide in Thlaspi calaminare ; whilst the ashes of the root, stem, and flowers contain 

 respectively 1-66, 3-28, and 3-24% of zinc. In Viola calaminaria and Armeria 

 vulgaris Risse found the largest quantity of zinc oxide in the root (1-52 and 3-58% 

 respectively of the ash). 



7. CALCIUM CARBONATE. 



i. ACTION OF CALCIUM CARBONATE ON THE METABOLISM 

 AND STRUCTURE OF PLANTS. 



Among the compounds of calcium in the soil are some important nutritive 

 salts, such as salts of nitric, phosphoric, and sulphuric acids ; also insoluble 

 completely indifferent substances such as calcium silicate (labradorite, 

 andradite, and others) ; and a salt, calcium carbonate, which although not 

 reckoned as a plant-food, yet affects the metabolism of plants and con- 

 sequently the character and composition of the vegetation. 



Lime combined with carbonic acid occurs in nature as the insoluble and 

 neutral calcium carbonate CaCO ;5 and as the soluble bicarbonate CaC 2 G H 2 1 . 

 The former salt cannot, on account of its insolubility, gain admission to 

 plants ; but on the other hand, the acid salt, which results from the action 

 of water containing carbon dioxide on the neutral salt and therefore 

 constantly accompanies it in the soil, is, as water-cultures attest, taken up 

 by the plant and apparently undecomposed reaches the water-channels, 

 the sap of which usually contains calcium carbonate. On the other 

 hand, it is very probable that the calcium carbonate often richly stored in 

 the cell-walls of active plant organs, for instance in cystoliths, arises as 

 a secondary product from other compounds of calcium, for example 

 from the calcium pectate which is always present in cell-walls a or by 

 double decomposition from the nutritive calcium salts (nitrate, sulphate, 

 or phosphate). The calcareous coatings of many green aquatic plants 



1 According to another theory, the bicarbonate does not occur in nature, but lime- 

 water rather contains the ordinary calcium carbonate and free carbon dioxide. This 

 question is without importance in geographical botany. 



2 The formation of calcium pectate in living cells is certainly ascribable to processes 

 similar to those for calcium oxalate, malate, &c. ; cf. Schimper, I, II. 



