The root-system.—The root-system of grasses is very striking in its character. In most grasses, especially in erect ones, several roots all of about the same diameter arise in a dense tuft from nearly the same level and from the lower-most nodes of the stems. The roots are all thin and fibrous in the vast majority of these plants, and they are tough and wiry only in a few cases such as in the case of the roots of Pennisetum cenchroides, P. Alopecuros, Ischæmum pilosum and Andropogon Schœnanthus.
On a close examination it will become evident that all the roots of a grass plant are adventitious. Inasmuch as the growth of the primary root is soon overtaken by other roots growing from the stem, all the roots happen to be of the same size. Roots arise from the nodes just above the insertion of the leaf, and they grow piercing the leaf-sheath.
Fig. 6.—Panicum Crus-galli.
Grasses in which stolons and prostrate branches occur have, in addition to the usual radiating crown of roots at the base, aerial roots growing out of the upper nodes of the branches and fixing them to the soil. Such roots become supporting or prop roots and are particularly conspicuous in several stout tall grasses such as Andropogon Sorghum, Zea Mays and Pennisetum typhoideum. (See figs. 8 and 9.)
All the roots bear branch-roots which originate from the inner portion of the mother roots in the usual manner. The character and the extent of the development of the root-system is to a large extent dependent upon the nature of the soil and its moisture content. In light dry soils roots remain generally stunted and in well drained rich soils they attain their maximum development. In clayey soils roots penetrate only to short distances. When the soil is rich and sandy roots go deeper and extend in all directions. The root-systems of most grasses are superficial and so are best adapted for surface-feeding.
Fig. 7.—Panicum javanicum.