. The ecological relations of roots . h penetrate every crevice of the gravelly soil. Fewif any of the grasses examined had such great masses of delicate clusters ofabsorbing rootlets. Such a grass is excellently adapted to live in the half-gravel-slide, as more thorough occupancy of the soil can scarcely be color the roots are bro-v\Ti to light tan. They were removed from thegravelly soil with no great difficulty. Kceleria cristata.—This grass, which is a characteristic dominant of thehalf-gravel-slide, is distinguished by an extremely fibrous root system. Themain roots at their o
. The ecological relations of roots . h penetrate every crevice of the gravelly soil. Fewif any of the grasses examined had such great masses of delicate clusters ofabsorbing rootlets. Such a grass is excellently adapted to live in the half-gravel-slide, as more thorough occupancy of the soil can scarcely be color the roots are bro-v\Ti to light tan. They were removed from thegravelly soil with no great difficulty. Kceleria cristata.—This grass, which is a characteristic dominant of thehalf-gravel-slide, is distinguished by an extremely fibrous root system. Themain roots at their outset vary from to mm. in diameter. At a depthof 1 to 4 inches many pf these run off parallel with the surface to a maximumdistance of 12 inches. These are branched and rebranched to the thirdand fourth order, the ultimate termini being almost microscopic in size(plate 26, a). Gilia aggregata.—The long pink or red racemes of this abundant biennialare very conspicuous on the half-gravel-sUde, where the plant is quite abun-. THE HALF-GRAVEL-SLIDE COMMUNITY. 97 dant. Of the 6 plants examined all had a large tap-root from 4 to 8 mm. indiameter. The tap sends off numerous branches near the surface and tapersso rapidly that at a depth of 10 inches it seldom exceeds 1 or 2 mm. in laterals are mostly wide-spreading, frequently nearly horizontal in posi-tion, and much forked and rebranched into very abundant fine termini. Theyreach distances of over a foot from the base of the plant. Like most plants ofthis habitat the root system is not deep. No Gilia roots were found below the28-inch level, but the moist surface soil is well filled with great quantities offine absorbing rootlets, especially to the depth of 18 inches. Potentilla arguta glandulosa.—This species frequently forms families on thehalf-gravel-shde. A large clump of these plants was examined. The com-plexity of the rootstocks is such that they are hard to describe. The individualclumps are connected
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