FUNCTION.] MAGNESIA ALKALIES. 277 



a vigorous vegetation. In many districts of Piedmont, where 

 the bi-carbonate of lime and of magnesia are abundant, the 

 cultivated lands produce beautiful plants. Hence he con- 

 cludes, 1st, that native carbonate of magnesia is not inju- 

 rious to plants ; 2nd, that, on account of the solubility of 

 magnesia in an excess of carbonic acid, that earth may exer- 

 cise an action analogous to that of lime ; 3rd, that magnesian 

 soils may be fertile when the necessary manures are employed. 

 M. Abbene is of opinion, from comparative experiments, that 

 the influence of magnesia on vegetation is analogous to that 

 of lime. He states that native magnesia is not injurious 

 to germination, vegetation, or fructification, but on the con- 

 trary, is favourable to those functions. Being soluble in an 

 excess of carbonic acid, it has an effect on vegetation similar 

 to that of lime. When land contains magnesia not sufficiently 

 carbonated, the defect is remedied by manure, whose decom- 

 position furnishes the necessary supply of carbonic acid. 

 When lime and magnesia co-exist, the former is absorbed in 

 preference, on account of its greater affinity for carbonic 

 acid ; when magnesian lands are barren, it is not to the mag- 

 nesia that the sterility must be attributed, but to the cohesive 

 state of its parts, to the want of manure, of clay, or of other 

 matters, to the presence of a large quantity of oxide of 

 iron, &c. 



Alkalies. All plants contain alkalies, in combination with 

 organic acids : and much probability attaches to the opinion 

 of Liebig that their office in a physiological point of view is 

 to form bases for those acids. In the majority of land plants 

 Potash predominates, in marine or maritime plants, Soda. 

 Liebig asserts that the proportion of these bases in a given 

 plant is invariable, but that any one may be substituted for 

 another, the action of all being the same. Since, however, 

 the quantity of alkali contained in different species is variable, 

 one species of plant will require a more alkaline soil than 

 another. The perfect development of a plant is therefore 

 dependent on the presence of alkalies or alkaline matter ; for 

 when these substances are totally wanting, growth will be 

 arrested ; and when they are deficient, it must be impeded in 

 proportion. 



