ch. i] The Morphology of Grasses 9 



flanking the mid-rib, or at the base of the grooves between all 

 the ribs. They are known as motor cells (see Figs. 8 and 10). 

 The special function of these cells must be left till the next 

 chapter, but it may be noted here that the transparent lines 



Fig. 12. Typical outlines of leaf -blades. Left to right: — Dactylis glomerala 



(broadest near base), Bromus sterilis, Poa trivialis, P. annua, P. pratensis 



(edges almost parallel throughout), Brachypodiwm syivaticum (tapering 



above and below), Holcus lanatus, Agrostis stolonifera, Festuca rubra 

 (needle-like). 



frequently seen running longitudinally between the ribs are 

 largely due to the presence of these motor cells. The higher the 

 ridges and the more these motor cells are developed, the greater 

 will be the contrast in opacity observed between the ribs and the 

 grooves when a blade is held up to the light. 



