Chap. V] THE SOIL 95 



are, on the contrary, certainly produced by the decomposition of the 

 bicarbonate and the precipitation of the insoluble neutral salt, resulting 

 from assimilation 1 . 



Calcium carbonate is present in all soils and in all waters, and in small 

 quantities is endured by all plants. No appreciable action on physiological 

 processes occurs in such cases. On the other hand, a nutritive solution 

 rich in calcium is poisonous to many plants, whilst by others it is tolerated in 

 different cases to a greater or less extent. Those plants that tolerate larger 

 quantities of calcium carbonate have their metabolism likewise affected 

 by it, and consequently often undergo visible structural modifications. 

 Calcium carbonate thus acts as do sodium chloride, serpentine, and 

 calamine. 



The poisonous action of calcium carbonate on many plants is most easily 

 proved in the case of aquatic vegetation. A supply of water rich in calcium, 

 for instance, suffices, as Sendtner proved, in a short time to kill the species 

 of Sphagnum and is not less poisonous to other aquatic mosses. The 

 same holds true for many Algae that are otherwise common, if we may 

 judge by their constant absence from water that is rich in calcium. Many 

 terrestrial plants are scarcely less susceptible. Thus, according to Christ, 

 a mere sprinkling with water rich in lime suffices, in a short time, to kill 

 Drosera and most of the other plants associated with bog-mosses on peat- 

 bogs. According to the same investigator, Lomaria Spicant, Allosorus 

 crispus, Saxifraga aspera, Phyteuma hemisphaericum, Androsace carnea, 

 and many others behave in a similar way. On a substratum rich in lime 

 Kerner cultivated various plants that never appear on a calcareous soil : 

 ' they at once sickened and died without blossoming.' Among trees, the 

 sweet-chestnut and Pinus Pinaster cannot tolerate a calcareous soil ; accord- 

 ing to Chatin, even three per cent, of calcium in the soil is fatal to the 

 sweet-chestnut. 



Plants that tolerate large quantities of calcium owe this capacity, as in 

 the case of halophytes in relation to sodium chloride, to a power of 

 accommodation which is often associated with visible structural modi- 

 fications. The connexion between these variations and the influence of 

 calcium can be explained just as little, either physiologically or oeco- 

 logically, as the variations induced in Algae by solutions of common salt, 

 or as the production of peculiar varieties of plants on calamine and serpentine 

 soils. Possibly we may also include under the same category of chemical 

 influences certain modifications induced by parasitic fungi in Euphorbia, 

 Anemone, and other plants. 



The first experimental investigations into the influence of lime on the 

 structure of plants were carried out by Bonnier, after he had noticed that 

 Ononis Natrix, on soils poor in calcium, possesses a physiognomy different 



1 Pringsheim, op. cit. 



