94 



THE FACTORS [Part 



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

 from that of other neighbouring localities by the assemblage of plants composin, 

 its flora. Viola lutea is completel3' absent from the Rhine countn,-, and is first seei 

 near Lieo-e. Alsine verna. also common on calamine soil near Aix, is still furthe 

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

 calamine soils, and Silene inflata, van glaberrima, is surprisingly abundant ani 

 luxuriant in places that are richest in zinc. 



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

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

 respectively i-66, 3-28, and 3-24% of zinc. In Viola calaminaria and Arnieri 

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

 respectivelj' 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 nutritiv 

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

 completely indifferent substances such as calcium silicate (labradoritf 

 andradite, and others) : and a salt, calcium carbonate, which ahhough no 

 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 anc 

 neutral calcium carbonate CaCO , and as the soluble bicarbonate CaCoOgHj 

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

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

 of water containing carbon dioxide on the neutral salt and therefor 

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

 by the plant and apparently undecomposed reaches the water-channel 

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

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

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

 a secondary product from other compounds of calcium, for exampl 

 from the calcium pectate which is always present in cell-walls - or b; 

 double decomposition from the nutritive calcium salts (nitrate, sulphatf 

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



' According to another theor)', the bicarbonate does not occur in nature, but limt 

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

 question is without importance in geographical botany. 



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

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



