Vl] MARSH AND AQUATIC ASSOCIATIONS 161 



The Relation of Mineral Salts to the Flora 

 AND Vegetation 



It will be seen that the difierences between the flora and 

 vegetation of the calcareous and the non-calcareous terrestrial 

 soils are paralleled by differences between the aquatic and 

 sub-aquatic flora and vegetation. These differences cannot be 

 explained by the differences in the physical nature of the 

 habitat, for, in the case of the tAvo aquatic habitats, the physical 

 characters are identical. The facts therefore support the view 

 that the presence of lime-loving plants in calcareous waters 

 and soils is somehow related to the chemical composition of 

 the waters (cf. Schimper, 1903: 102). Wheldon and Wilson 

 (1907 : 90) also point out that in addition to water-content, 

 " another agent also has its influence. On examining the 

 plant associations of habitats having about the same degree 

 of humidity, we frequently lind the species in them are totally 

 dissimilar." These authors then go on to give the groups of 

 species found respectively in boggy ground at the calcareous 

 shore of a moorland tarn, with Primula farinosa, Cladium 

 Mariscus, Schoenus nigricans, Jimcus obtusiflorus, and Hypnum 

 falcatum ; of the swampy margin of a pool on the glacial drift, 

 with Ranunculus Flammula, Bidens tripartita, Alisma Plantago, 

 Sparganium neglectum, and Hypnum aditncum ; of a peat bog, 

 with Drosera spp., Andromeda Polifolia, Carex limosa, Myrica 

 Gale, and Sphagnum spp. ; and of estuarine marshes, with 

 Spergidaria media, Limonium (= Statice), Aster THfolium, and 

 Glyceria maritima. As " in all these stations the water supply 

 is fairly constant and really in excess of plant requirements, 

 and the conditions of altitude and exposure practically identical," 

 the authors " are led, therefore, to the conclusion that some 

 component of the soil must be the factor which determines the 

 presence or absence of these various species " ; and it seems to 

 me also that a study of the distribution of plants in any district 

 where the chemical composition of the soil shows gi-eat varia- 

 tions leads inevitably to the conclusion of Nageli (1865: 367), 

 of Schimper (1903: 101), and many others that the chemical 

 constituents of the soil, in addition to any or all of the physical 



M. 11 



