Minnesota Plant Life. 



481 



By substratum he means the soil, whether it be rich in calcium, 

 sodium or nitrogen. By neighbors he means the surrounding 

 plants and animals which by their proximity affect the habits 

 or structures of the plant in question. Thus, in accordance 

 with the origin of their most characteristic adaptations, he 

 divides vegetation into three fundamental groups, viz., climatic 

 formations, substratum formations, and neighborhoods. Desert 

 plants, for instance, may be grouped among the climatic, salt- 

 succulents among the substratum, and carnivorous plants among 



FIG. 240. View of Fort Snelling, showing midsummer vegetation. After photograph 



by Williams. 



the neighborhood formations. The further extension of such 

 a classification is perhaps sufficiently apparent without multi- 

 plying examples. Aquatic plants would form a special class. 



Yet under even so general an analysis it must be evident that 

 very many plants indeed, most of them will appear in one 

 group or another, as attention is diverted to one or another 

 aspect of their adaptation. The tree-top orchid as an air-plant 

 falls into the group of climatic formations, but as a plant en- 

 abled through the cooperation of its root fungi to use decaying 

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