ROOT SYSTEMS OF TRUE-PRAIRIE SPECIES. 21 



comes especially dominant during seasons with an excess of rainfall, it is not 

 easily destroyed by drought. During a dry time it ceases growth, and as a 

 result of protracted dry periods may even become brown and apparently dead, 

 but upon the advent of rain it quickly revives. Its ability to withstand tramp- 

 ling and its early growth in the spring, as well as late in the fall, make it an 

 excellent pasture grass over wide areas in the true and subclimax prairies. 

 However, its cessation of growth during dry midsummers is very disadvanta- 

 geous to the stock raiser. A study of its root habit affords a much better 

 understanding of its growth and its success as an invader in stabilized vegeta- 

 tion. It is a species exceptionally well adapted for absorption in the surface 

 soil, but in times of drought it must rely to a large extent upon absorption by 

 the deeply penetrating roots. 



Spartina cynosuroides. — This tall, coarse grass of low lands is a dominant 

 in the subclimax prairie (Clements, 1920), and also occurs in moist areas in 

 true prairie . Its rank growth and dense sod-forming habit frequently exclude 

 other plants entirely. It is an indicator of land with a high water-content. 

 This species was excavated in alluvial soil near the station on the low prairie 

 at Lincoln, where it formed a pure growth over a limited area. The first 6 

 inches of soil is filled with a mat of coarse, woody, very much-branched rhi- 

 zomes from 5 to 10 mm. in diameter. They vary greatly in length, some ex- 

 tending only 2 or 3 inches and others over 12 inches before giving rise to erect 

 shoots. They are covered with long, dry, overlapping leaf -scales; the younger 

 ones, especially, are tipped with long, sharp-pointed buds. From the base of 

 the clumps the roots arise in groups of 2 to 5 or more. They also originate, 

 usually singly, at distant intervals along the rhizomes. They are very coarse 

 and tough, some measuring 3 or 4 mm. in diameter. They taper so gradually 

 that at a depth of 7 to 8 feet they are still 1 to 1.5 mm. thick. Some 

 were traced to a maximum depth of 9 feet and may have penetrated a foot or 

 two deeper, but at this level the water seeped so rapidly into the trench as to 

 prevent further excavation. In general, their course is vertically downward, 

 although they zigzag frequently through distances of 0.5 to 6 inches (fig. 4). 

 The branches may run off rather horizontally for 5 or 6 inches and then con- 

 tinue downward. The soil beneath the plant is quite filled with roots, es- 

 pecially the first 5 feet, and many extend to the water-level at 9 feet. The 

 laterals are threadlike and very abundant, usually an inch or less in length, 

 crooked and poorly rebranched. However, some of the branches reach lengths 

 exceeding 3 inches. The ultimate branches are usually only a few millimeters 

 long. This grass has the coarsest roots of any examined. Its great depth of 

 penetration is surprising when the water relations of its habitat are considered 

 (cf. table 3). 



Salvia pitcheri. — This sage occurs throughout the grassland communities 

 from Minnesota to Texas. It is conspicuous from July to September, when 

 the tall plants, which often form societies, overtop the grasses. The large 

 blue flowers lend pleasing variety to the purple and yellow of blazing-stars, 

 goldenrods, and sunflowers. Several specimens 4 feet tall and in full bloom 

 were examined near the high-prairie station at Lincoln. This autumnal 

 bloomer has a short woody rhizome usually not over 10 mm. in diameter and 

 often only 1 to 3 inches in length. From the base of the plant and from the 

 rhizome there arise many tough, rather woody roots. As many as 18 of these 

 were counted on a single inch of the rhizome. These vary from 4 mm. to less 

 than a millimeter in diameter, many being about 2 mm. thick. The older 

 ones are nearly black in color, with a bark which peels off rather easily; the 



