Plant Communities of the World 275 



tion" covers the middle altitudes. Species of Quercus and Arcto- 

 staphylos and others are preponderating. 



7. Ericifruticeta: Ericaceous scrub (heaths). — Ericifruticeta are 

 scrub communities whose dominants bear ericoid leaves. The 

 cricoid, rolled-up structure gives a tubular form which makes 

 the leaves stiff without the necessity of special mechanical tissue. 

 The heaths hve in a cool, moist, oceanic climate. They are ex- 

 tremely well developed in Norway, and they follow the coast 

 regions of Great Britain, Germany, and France to the Canary 

 Islands, through cool, oceanic, subalpine belts of mountains. 

 They look xeromorph, but Stocker has proved that they are 

 mesophytes to hygrophytes. These studies have proved that we 

 were right in placing these communities here by their habitat, 

 at a time when the ecology was yet far too little known. The 

 smallness and ericoid form of the leaves stiffens them against 

 being torn and wilted by the very heavy winds of these countries. 

 The xeromorph appearance is an unintended by-eif ect. The soil 

 is leached and poor in salts; and heavily transpiring evergreen 

 heath scrub gets out the best of it, as the vegetative season is 

 prolonged by the oceanic climate with mild winters. Calluna 

 heath was the association which awakened the first phyto- 

 sociological ideas in Alexander von Humboldt. It occurs on 

 wide stretches in Great Britain, the Netherlands, northwestern 

 Germany, and southwestern Sweden. A moister association is 

 the Ericetum tetralicis; a special Cornwall heath is the Ericetum 

 vagantis. Other heath communities are found in Portugal, in 

 the upper part of the fog belt of the Canary Islands, and else- 

 where. A well-developed heath system are the arctic and the 

 alpine dwarf shrub communities. Remarkable for richness in 

 species (about four hundred species of Erica) are the heaths of 

 Cape Province. 



