52 



THE ECOLOGICAL RELATIONS OF ROOTS. 



Another plant had a caudex 3 inches in diameter which reached a depth of 

 23 inches. Here it was still 2 inches thick. It branched into two equal 

 laterals. These were much flattened and distorted, one being less than an 

 inch thick but 2 inches wide. These branched and rebranched, as showoi in 

 plate 18, c, all ending within a horizontal distance of 16 inches from the base 

 of the plant. Each was abruptly tipped with a bud. These deeper branches 

 were not so well provided with roots as was the upper part of the stem. 



Agropyrum glaucum. — ^Wheat grass, if at all abundant, is an indicator of 

 favorable deep soil-moisture conditions. However, in thin stands and as 

 dwarfed individuals it occurs in rather dry places. The plants here described 

 were growing in low ground near a ravine. 



The tufts of these coarse plants are connected by stout, tough rhizomes 

 about 2 mm. in diameter and from a few inches to more than 18 inches in 

 length. From the base of these clumps and from the rhizomes, which lie at a 

 depth of about 1 inch, arise mmaerous short horizontal roots. These are pro- 

 fusely branched and rebranched to the third and fourth orders, the ultimate 

 branches being almost microscopic in size, and thus furnishing a splendid 

 surface absorbing system. 



An abundance of coarse, tough roots, from 1.5 to 2 mm. in diameter, pene- 

 trated in a more or less vertical direction and others at an obUque angle to a 

 maximum depth of over 7 feet. These coarse roots are covered with a brown 

 papery cortex, rather readily removed from the large wire-hke nearly white 

 stele. These roots are profusely branched with laterals from a few milli- 

 meters to 2 or 3 inches long, many of these branches running off more or less 

 horizontally. At a depth of about 4 feet many of these roots become only 0.2 

 mm. in diameter, but the branches (which are somewhat shorter) are no less 

 abundant to the very tip. The roots have such an abundance of root hairs 

 that the whole surface appears to be covered with wool. Thus Agropyrum 

 is suppHed with an absorbing system which thoroughly permeates all portions 

 of the soil to a depth of 6 feet. 



Carex pennsylvanica. — ^This sedge has a wide range throughout the grass- 

 land formation. Because of its early growth and flowering habit, it forms 

 conspicuous societies in the prevernal aspect, often before the taller gi*asses 

 resume growth. 



The roots of a number of plants of this species were examined. The tufts 

 are connected by coarse rhizomes, 2 to 10 inches long, at a depth of 1 to 3 

 inches. The much-branched flbrous roots have a lateral spread from the base 

 of a tuft of only 2 to 3 inches. They originate from the rhizomes as well as 

 from the base of the clumps. While many of the roots, after sending off 

 abundant laterals which branch to the third and fourth order, end at a depth 

 of 12 to 14 inches in exceedingly well-branched tips; others penetrate deeper. 

 A few roots were traced to their delicate endings at a depth of 3 feet, while 

 others occurred below the second foot. The chief absorbing area lies within 

 the first and second feet of soil. 



Andropogon scoparius. — The httle bluestem occurs throughout the grass- 

 land formation wherever enough water is present to support its growth. In 

 the drier plains association it is often confined to slopes mth a rough topog- 

 raphy and greater water penetration or to sandy soil. It dominates the short- 

 grasses under the latter soil condition and forms an extensive bunchgrass 

 consocies. Under the still more favorable moisture-supply of the prairies it 

 abandons the bunch habit and becomes a sod-former. The lateral spread of 

 the roots is about 1 foot on each side of the plant and within 4 inches of the 

 surface. The roots are very abundant up to the very surface, thus affording a 



