VEGETATIVE ORGANS OF GRASSES 343 



growths more conspicuously than any of the others. Bromus in- 

 ermis, Elymais robustus, Koeleria cristata, and Phleum pratense 

 failed to grow either in the laboratory or in the greenhouse. 

 This might have been due to any •number of possible causes, the 

 most probable of which was failure to obtain a vigorous rhizome 

 for planting. All of the figures were drawn from specimens of 

 the greenhouse grasses, so that they are representative of uni- 

 form conditions. 



Many of the grasses had resting periods. Striking illustrations 

 of those having rest periods, are, MuJdenbergia Mexicana, MuM- 

 enhergia racemosa, Sparfitia cynosuroides, Stipa spartea. The 

 two species of Muhlenbergia had resting periods of four months, 

 while the resting periods of the others were two months. All of 

 the other grasses began to gTow within three, weeks, but none of 

 them grew vigorously until j\Iarch. 



DEFINITION OF TERMS USED IN THIS DISCUSSION. 



The use of the term "grasses" is restricted to those plants 

 classed as Graminege. The Carex is used here as a means of 

 contrast. The grasses may be distinguished from sedges by the 

 following characters: stems .jointed, unusually hollow, leaves in 

 two ranks, alternate, the leaves consisting of the blade, sheath, 

 ligule and collar. The blade is narrow and elongated ; 

 iiheath, tubular in structure, usually enclosing the stem; the 

 ligule, a membranous appendage at the base of the blade. The 

 rhizome or rootstock consists of a thickened underground stem, 

 by which, the grass may perpetuate its growth and from which 

 arise the true roots. Thus the perennial grass plant may be said 

 to consist of root, rhizome, culm, leaf and flow^er. A perennial 

 grass may be distinguished from an annual by the presence of 

 the rhizome. It is frequently difficult to distinguish the rhizome 

 of a perennial. But instead of a creeping rhizome as in the 

 Agropyron repens there is developed a thickened basal portion 

 from which buds arise, as in Hordeutn jubaiuyn. Generally this 

 type of abbreviated stem, which may be classed as a short lived 

 perennial or winter annual, sends out an abundance of fibrous 

 roots. _ In case of the Phleum pratense the thickened base is a 

 rudimentary corm.^^ Again, there is the type of rhizome rep- 



i^Kraemer, Henry, Botany and Pharmacognosy, p. 105. 'A corm is inter- 

 mediate between a true tuber and a bulb, it is more in tlie nature of a tliick- 

 ened internode, being surrounded in some cases by thin membranous scales' 

 as in Phlmtm pratense. w 



