222 



PLANT PHYSIOLOGY AND ECOLOGY 



little importance or absent, as in deserts, wastes, denuded areas, 

 bogs, ponds, etc., the facies consist of other herbaceous plants. 

 In meadows, prairies, and plains, howeA'er, the rule is almost in- 

 variable that the dominant grasses alone are the facies. The 

 latter are not necessarily the most conspicuous species of the 

 formation. This is true in the case of forests and thickets, but in 

 meadows and prairies other herbs often overtop and conceal the 

 grasses. This is usually true for only a part of the growing period, 



Fig. 82. The spruce forest formation (Picea and Pseudotsuga) at 

 Minnehaha, near Pike's Peak. 



and at all other times such species are subordinate to the grasses, 

 which always form the groundwork of the formation. 



237. Principal and secondary species. The rank of the remain- 

 ing species is determined largely by their abundance, with some 

 reference to their size. The most abundant and characteristic, 

 the facies excepted, are termed principal species, while those of 

 less importance are secondary species. The line between the two 

 groups must be fixed more or less arbitrarily. Abundant con- 

 spicuous species can be readily referred to the first group, just as 

 sparse and inconspicuous ones belong to the latter. Between 



