THE PLANT FORMATION 



223 



these lie the species of more or less importance. The order of 

 these is determined by their abundance, and the place at which 

 the line is drawn between principal and secondary species must 

 be decided with reference to the species concerned. 



238. Aspects. The general appearance of a formation changes 

 more or less with the season. It usually has a different stamp 

 during each season, and is said to show seasonal aspects. These 

 are determined by the principal species which bloom at the season 

 concerned, and give a particular impress to it. The facies take 



Fig. 83. Early aspect of the alpine meadow formation, characterized l>y 



Rydbcrgia (jrundiflora. 



practically no part in this in the case of woody formations, where 

 the seasonal change affects only the undergrowth. This is true 

 to some extent in grasslands in which the facies are more or less 

 obscured by taller herbs, though the flowers of the grasses play 

 an important part in one of the later asi)ects. 



The growing period is usually divided into four aspects, cor- 

 responding to the periods of flowering. These are the early sjiring, 

 the spring, summer, and autumn aspects, which arc also calle^l 

 prevernal, vernal, estival, and autumnal. In high mountain 



