WATER CONTENT ASSOCIATION 21 



but also termed Bruchpflanzen!; (3) "plants that love a dry 

 soil {plantae soli aridi). In distinguishing plants with respect 

 to medium, Schouw divided water plants into ptantae vera 

 aquaticae s. plantae submersae, which he termed Hydrophyta, 

 and plantae aquaticae spuriae sive plantae emersae. The groups, 

 plantae marinae and plantae aquae dulds, are based upon the 

 chemical properties of the water, and the second group is 

 further analysed into plantar lacustres, fluviales, fontanae, 

 stagnariae, etc. Species growing m saline situations are 

 represented by strand plants (plantae littoralis v. maritimae), 

 while, in arranging plants according to the chemical nature 

 of the soil, salt plants are designated as plantae salinae, 

 Halophyta. Meyen (J 836:50), though in the main following 

 Schouw very closely, includes all aquatic plants under 

 Hydrophya. To Thormann (J849) belongs the great credit of 

 perceiving, at a time when the chemical nature of the soil 

 was thought to determine the character of the vegetation, 

 that the physical properties really control the water content, 

 and are hence of the first importance. He divided soils into 

 two classes ; eugeogenous, those that disintegrate readily and 

 completely , and hence are water-retaining, and dysgeogenxms, 

 those that strongly resist weathering and decomposition, 

 and in consequence lose water readily. Plants growing on 

 eugeogenous soils were termed hygropMlous, and those in 

 dysgeogenous soils, xerophilous, while those which seem to 

 grow indifferently in either were called ubiquitous. Thur- 

 mann understood clearly that it was the degree of decompo- 

 sition and aggregation, and not the chemical nature of the 

 rocks, which determined the last group, as so-called 

 silicious species were found to grow on calcareous soils when 

 these were loose, and calcareous species on silicious soils 

 that had become compact. A. De CandoIIe (1855:423), with- 

 out attempting a grouping of plants with reference to water 

 content, which lay outside his field of botanical geography, 

 none the less clearly noticed this fundamental difference 

 in soils, as the following will show : ' 'Ily a des min^raux 

 qui se r^duisent plus ou moins facilement en terre ou en 

 sable, et qui offrent des conditions de t6nacit6 particuliferes : 



