2. The presence of certain atypical soils (such as serpentine, 

 acid clays, etc.) may result in the presence of a plant community 

 that is not typical of the general area. 



3. The restriction of a plant species or a race to a specific soil 

 type may be due to genetically determined physiological adapta- 

 tion to this soil as well as to an inability of the plant to survive 

 naturally on other soil types. 



4. The absence of a plant species (or race) from a soil type 

 present within its geographical range is probably due to a geneti- 

 cally determined intolerance to this soil type. 



5 . A plant species that occurs on a wide variety of soils can 

 do so because it is made up of ecological races that are individu- 

 ally adapted to these soils. Each ecological race may have a 

 narrow adaptation, and one result of this is that the ecological 

 ampHtude exhibited by a species is a rough reflection of its 

 ecotypic richness. That is, a species that occupies a wide range of 

 habitats is likely composed of more ecological races than is a 

 species which occurs in a more restricted variety of habitats. Thus, 

 in general, the ability of a species to occupy a wide range of 

 habitats is due to the presence in the species of ecological races, 

 otherwise called ecotypes. 



There are different kinds of ecotypes. For example, Gilia 

 capitata contains at least two different soil ecotypes, one adapted 

 to serpentine soils, the other to non-serpentine soils. Lasthenia 

 minor likewise has two soil ecotypes: one of these (sufficiently 

 distinct in its external morphology that it is recognized as a 

 taxonomic subspecies) occurs only on guano (Plate 4C) and the 

 other (another subspecies) is on non-guano soils. There are also 

 climatic ecotypes, that is, races of species adapted to different 

 climates within the range of the species. Many wide-ranging tree 

 species are made up of climatic ecotypes, as are several herbaceous 

 species (such as Yarrow) that occur from sea level to above 

 timberline in the Sierra Nevada. There are also seasonal ecotypes: 

 in the California tarweed Madia elegans there is one spring-flower- 

 ing ecotype and another fall-flowering ecotype. 



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