CH. I] 



The Morphology of Grasses 



the enlarged bases of the sheaths (Fig. 2). They are usually 

 smooth, but may be striated, i.e. have prominent longitudinal 

 ridges. 



The sheath may form a cylindrical tube enclosing the stem — 

 when it is said to be "entire," or the margins may be more or less 

 membranous and overlap one another, in which case the sheath 

 is said to be "split." Generally it is only possible to be certain 



Fig. 5. Portion of plant of Poa pratensis showing its extensively creeping 

 rhizome3 producing separate tufts of foliage. The true (fibrous) roots are 

 seen to arise from the nodes of the rhizomes. 



whether a sheath is " entire" or " split" in the case of the sheaths of 

 the flowering stems, and even in these the sheaths may often be 

 mechanically torn away for an inch or two at the top. 



The shape of the young sheaths — and therefore of the young 

 shoot — is determined by the arrangement of the leaf-blades in the 

 shoot (Figs. 6 and 7). If the blades are folded (conduplicate) the 

 sheaths are more or less flattened or compressed, and usually then 

 have acute edges or keels. If the blades are rolled (convolute) in 



