MORPHOLOGY OF THE VEGETATIVE ORGANS 101 
Between species with well-marked rhizomes such as 
described above and species in which the rhizomes are 
absent there are many transitions. The rhizomes may be 
short and thick with the scales close together, the plants 
forming loose tufts. Or the rhizomes may be slender but 
short and ascending, the plants also forming loose tufts. 
In certain species, usually classed as bunch-grasses, in 
which the tuft grows by accretions at the outer edge, the 
new shoots must bend outward and upward to reach the 
light. In large tufts the outer shoots have decumbent 
bases which may simulate short rhizomes. In some 
cases, especially in desert regions, such tufts may assume 
the form of fairy rings, dying out at the center and expand- 
ing at the circumference, until finally the living zone 
breaks up into isolated tufts, each to become a new center 
of growth. 
126. Stolons—wWhen the modified propagating stems 
are produced above the surface of the soil they are called 
stolons or runners. They differ also from rhizomes in that 
they bear foliage-leaves instead of scales, although these 
leaves are usually different in size or shape from those 
produced upon the foliage-shoots. Stolons are to be dis- 
tinguished from shoots of creeping prostrate or decumbent 
plants in that they are modified creeping stems, that 
is, they differ from the ordinary erect or ascending shoots 
of the same plant and have the distinct function of 
propagation. The buffalo-grass produces stolons so abun- 
dantly that the plant forms a firm sod upon large areas of 
the Great Plains (Fig. 48). It was from such sod that 
pioneers in this region made their sod houses. In the 
tropics stolon-producing species are more numerous than 
in the cooler regions. Pard-grass, when growing in new 
soil, produces vigorous stolons as much as 20 feet long. 
