134 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA. 



virgatum, and Elymtis canadensis, with Spartina in the moister areas (cf. 

 Pool, 1913 : 298). The growth-forms are in almost perfect accord with the 

 factor and serai sequence. Spartina, which is both hydroid and the earliest 

 in appearance, has a growth-form usually 5 to 7 feet and sometimes 8 to 10 

 feet high. Andropogon furcatus and A. niUans are normally 4 to 6 feet and 

 occasionally 6 to 8 feet tall, while A. saccharoides is a Uttle shorter. Elymus 

 canadensis and Panicum virgatum are practically the same height, from 3 to 



5 feet. Andropogon scoparius is usually about 3 feet in height and Bouteloua 

 racemosa generally somewhat less. In size and habit, A. scoparius is the 

 transition form to the true prairies, in which the dominants are between 2 and 

 3 feet high. This also explains why it is such a constant associate of Stipa 

 and Koeleria. The root relations are less distinctive, as would be expected. 

 Andropogon furcatus and Panicum virgatum are the most deeply rooted, A. 

 nutans and A. scoparius come next, wliile Elymus canadensis resembles Koeleria 

 and Stipa in having shallow roots (Weaver, 1919). 



Grouping. The dominants which constitute the greater part of the associa- 

 tion are A. furcatus, A. nutans, and A. scoparius. Mixed or alternating, they 

 occupy nine-tenths of the area and form the pattern in which the others play 

 minor parts, except in localized areas. The actual groupings are best shown 

 by the records of 33 quadrats charted by Thornber (1901 : 95) in the south- 

 eastern corner of Nebraska, and ranging from wet meadow to hilltops. Of 



6 quadrats in the wet meadow, 4 contained Spartina cynosuroides and 5 

 Poa prcUensis as dominants. The 5 quadrats in the meadow or low prairie 

 all contained A. furcatus and A. scoparius; 3 contained A. nutans, and 3 

 showed Elymus and Panicum. With regard to the number of dominants, 2 

 quadrats showed all five; 1 showed four, and 2 showed three. A. furcatus and 

 A. scoparius occurred as dominants in every one of the 22 quadrats on the 

 slopes and crests, Bouieloua racemosa in 4, Koeleria cristata in 2, Pani- 

 cum scoparium in 2, and P. virgatum in 1. P. scoparium also occurred in 

 more or less abundance in 17 other quadrats, B. racemosa in 14, Stipa spartea 

 in 12, and Koeleria cristata in 9, suggesting the transition to the true prairie. 

 Southward from Kansas into Texas, similar groupings of the dominants occur, 

 but A. furcatus is partly or largely replaced by A. saccharoides, while A. 

 haUii plays a r61e of some importance. 



SOCIETIES AND CLANS, 



These are all but identical with those found in the Stipa-Koeleriapraine and 

 it is unnecessary to repeat the listson pages 130 and 131. A few additions might 

 be made, but these are nearly all invaders from woodland and thicket and do not 

 properly belong in the prairie. Likewise certain societies derived from the 

 west or southwest, as Gutierrezia sarothrae, Grindelia squarrosa, and Artemisia 

 frigida, are Uraited to the western edge or are altogether lacking. An excellent 

 idea of the societies and clans of the subclimax prairie can be gained from 

 Thornber's treatment (1901). This author gives a detailed account of aspects 

 and treats the grouping and behavior of the subdominants on pages 54 to 95. 

 This is followed by an account of the many quadrats in both list and chart 

 form (pp. 95 to 136), and a phenological record of practically all the species for 

 1899-1900 (cf. Gates 1912 : 300, 327). 



