however, each species contributed one point each in the total of 

 two. Differences between the two methods for herbaceous 

 phanerogams are shown in the table on page 94. The fre- 

 quency-point spectrum in this region emphasizes the impor- 

 tance of the better-protected life-form classes as compared to 

 the species-list spectrum. The influence of the drier, more con- 

 tinental climate in Minnesota, in comparison to the moister 

 climate in the mixed mesophytic forests of the southern Appa- 

 lachians, can also be shown. ^^ 



Habitat-forms bear the impress of the habitat, such as cacti in 

 arid climates (Figure 3-1) or Elodea submerged in water. These 

 forms are mainly ecological and are of special value as indicators 

 of environmental conditions. They can also be used in the analysis 

 and characterization of communities, but have not been used ex- 

 tensively. The most common classification contains three classes: 

 hydrophytes, which include submerged, floating, and amphibious 

 plants; mesophytes, which include sun and shade plants; and 

 xerophytes, which may be divided into groups on the basis of 

 ability to endure drought. Every species has its own range of 

 ecological amplitude, so by knowing the kinds of species that 

 make up a stand one can evaluate the environmental conditions 

 to a considerable degree. For instance, a stand o{ Distichlis stricta 

 usually indicates a higher salt content and a shallower water- 

 table than a stand of this grass intermixed with Agropyron smithii, 

 while a stand of the latter as the sole dominant indicates little or 

 no salt. 



The detailed classification of habitat-forms by Iverson'^'* in- 

 cludes four main divisions: land, swamp, amphibious, and water 

 plants. The land plants comprise the following five classes: (1) 

 seasonal xerophytes, as Sedum spp., which have shallow root sys- 

 tems and considerable tolerance to endure long periods without 

 absorbing water; (2) euxerophytes with well developed root sys- 

 tems but which wilt quickly when absorption of water ceases, sub- 

 divided into four subclasses; (3) hemixerophytes with poorer root 

 systems which also wilt quickly, subdivided into four subclasses; 

 (4) mesophytes with poor, quick-wilting root systems; and (5) 

 hygrophytes, plants of wet areas such as the marsh marigold 



Aimalytic Characteristics of the ConrnrnniaxEmty * 95 



