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, d>ing 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. — When 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. Para-grass, when growing in new 

 soil, produces vigorous stolons ^ much as 20 feet long. 



