69 



large regular tufts, higher in the center; L^ptolonia cognatum 

 (Schultes) Chase, with large, compact, flat-topped tufts; Stipa spar- 

 tea Trin., tall, loose, few-leaved; Fanicum pseudopnbescens Nash, 

 with short, broad leaves, forming very flat bunches, often eighteen 

 inches in diameter; Boiiteloua hirsuia Lag., very depressed, grayish 

 bunches, which are often subordinated by other grasses; one, pos- 

 sibly two, other species of Boiiteloua; Cyperus schzvcinitzii Torr., a 

 sedge fonning sparse, open bunches; Andropogon scoparius Michx., 

 and Andropogon furcatus Muhl., forming very large bunches. 



The bunch-grasses permit the growth of the secondary plants only 

 in the small areas of l)are sand between the bunches. These sec- 

 ondary plants form three ecological groups, which may be called per- 

 ennials, mats, and interstitials. 



The perennials are usually deep-rooted, most of them growing in 

 bunches like those of the grasses. These are usually able to with- 

 stand the encroachment of the grasses, but can not displace them. 

 The typical perennials are Aster linariif olius Linn., Lithospevmum 

 gnielini Michx., Aster sericeus Vent., Tephrosia virginiana (Linn.) 

 Pers., Chrysopsis villosa Nutt., Petalostenion (2 species), Physalis vir- 

 giniana Mill., Baptisia bracteata (Muhl.) Ell. The shrubs of the 

 association may be classed with this group. They are Rhus cana- 

 densis var. illinoensis (Greene) Fernald, which forms dense masses, 

 often building up small dome-shaped dunes, and Aniorpha canescens 

 Pursh and Ceanothiis aniericonus Linn., with large woody roots. 



The second group, the mat plants, is a small one, including only 

 Opuntia rafinesquii Engelm. (the common prickly pear) and a species 

 of Antennaria. 



The interstitial plants are usually annuals, and as the slender 

 stems occupy very little space, they have no part in the binding of 

 the sand. They are absolutely dependent upon the bunch-grasses. 

 The commonest of the interstitials are : Oenothera rhonibipetala 

 Nutt., Ambrosia psilostachya DC, Linaria canadensis (Linn.) Du- 

 mont. Cassia chaniaechrista Linn., Monarda punctata Linn., and 

 Croton glandidosus Linn., var. septentrionalis Muell. Arg. 



The animals of this association include most of the species char- 

 acteristic of sand prairie. 



PHYTOPHAGOUS ANIMALS OF THE: BUNCH-GRASS 



The plant-eaters are the basic group of the animal assemblage. 

 They are represented in all the habitats of the association, but are 

 most numerous in the plant stratum. 



