ISO 



grass on tlie sand-hills of Nebraska (Pound and Clements, '00. 

 p. 353). 



Next in importance as sand-hinders are certain species 

 which grow in close hemispherical or flattened bunches, and 

 hold the sand in the same manner as the bunch-grasses. Rhus 

 (iromafira (PI. XIX.) grows in dense thickets, sometimes twen- 

 ty feet in diameter, its long branching roots descending to a 

 depth of six feet or more, and effectually resisting the move- 

 ment of the sand. Craccii n'lyjiincd. LitlKispi-nitii iii li/ieiu-i/h/iuiii, 

 Sd/.i.r f/'i.sfis, C/iri/snpsis (■(iiiip(iniiit, and especially Aiiiorjilid 

 (■aiiescci/s, have the same habit as Rhus, but on account of their 

 smaller size are less effectual as sand-binders. 



SjxH'olioiiis cn/jif(i/i(/nis, and ('(iiiniit'iiini rliyii/ico have stems 

 prostrate and rooting at the nodes, and both are (juite effectual 

 sand-binders, although the latter species is not frequent, and 

 neither reaches a large size. Spoi-obolns is quite abundant on 

 level blow-sand, where it builds up mounds from four to eight 

 inches high (PI. XVIII., Fig. 2). It is one of the principal 

 species concerned in fixing blow-sand and preparing it for the 

 re-estaljlishment of the bunch-grass association. Conniu'li/Ki 

 also builds up small mounds and ridges of sand. 



A third type of sand-binders is composed of mat plants, 

 which have prostrate stems radiating from a central root. 

 Kiiphnrhid (iciicri is common on blow-sand, where it grows in 

 circular mats from six inches to two feet in diameter. It thus 

 effectually holds the sand l)eneath it. and is frequently seen on 

 a flat mound an inch of two high, closely similar in shape to 

 the plant itself. Molhiyo reiiiri/lafa, frequently naturalized on 

 blow-sand and in the bunch-grass, has the same habit. Opioif/a 

 hniiiifiisd may be classed in the same group. It forms dense 

 mats two to live feet in diameter, and effectually holds the 

 sand. The center of the mats, however, are frequently buried. 

 Arcnifes viridifioi'd. usually erect in a richer soil, is prostrate 

 when growing on blow-sand, and builds up small mounds. 



Intermediate between prostrate forms like the last and 

 bunch-forming species like Chri/sopsis are such plfints as Soli- 

 (Jayo inis.'iudriciisis, and ('aUirhoe tfhnujiihdd. These have sev- 



