Tgt7]} VESTAL—FOOTHILLS VEGETATION 359 
Dénsinant plants shrubs, or rarely reaching tree size 
Plants larger, comparatively well separated; plant unnosition variable; 
ranging also into xerophytic habitats 
Foothiils mixed shrub association 
Plants smaller, low, closely set, usually in fine moist soil 
Symphoricar pos association 
Dominant plants herbaceous. . . . Foothills mesophytic grassland association 
Descriptions of associations 
The plant communities are described in the order of their 
appearance in the foregoing synopsis. They are subject to greater 
geographic variation than can be treated fully in this article; 
mention is made, however, of the more considerable variations. 
The space allotment is not always proportionate to the importance 
or general interest attaching to the several associations; some are 
already fairly well known, some are less variable or can be summed 
up more concisely than others, and some have been less thoroughly 
or less widely studied. An approach to a balanced treatment has 
been sought by the use of a smaller type for statements of less 
general significance, descriptions of minor or very local vegetation 
divisions, and detailed passages included by way of illustration or 
amplification. 
Plant names, when appearing without citation of authorities, may be 
understood to be as in CoULTER and NELson’s Manual (2), which in general 
follows the usage recommended by the Vienna Congress. The unit of vege- 
tation is the plant association, in the generally accepted sense; its distinctive 
representations, appearances, or variants are spoken of as consocies; the terms 
as used are described in an earlier article (24, p. 382, footnote). Index letters 
attached to species names signify frequency or abundance or regularity of 
occurrence, as follows: a, abundant; f, frequent; 7, infrequent; /, focal or 
locally; ch, characteristic in the community or situation mention 
It will be understood that the total number of species of iat occurring 
in an area so extensive as that of this study is very large. No attempt has 
been made to work out the complete floristics, or the floristic variation of the 
several communities as represented in different localities. Field botanists 
will remember that very many of the species making up the flora of a region are 
rare, known from a single or very few stations, are in effect of very slight 
ecological significance, so far as vegetation is concerned. A further consider- 
able proportion is not found in extensive plant assemblages (as, in this study, 
grass species occurring only in stream margins), and is not important as part 
