THE STRUCTURE OF GRASSES 47 



Leaf. — The leaves are the foliage organs of the plant. 

 They may be crowded in tufts as already described or 

 may be scattered along the stem. In our common 

 meadow and pasture grasses the stems remain short in 

 the early part of the season and the foliage is thick and 

 tufted close to the ground. Later the long flower stems 

 are produced. After the ripening of the seed the flower 

 stems wither away and during the remainder of the season 

 the grass continues in the tufted condition. 



The leaves invariably arise from a node or joint of a 

 stem, one leaf to each node. This arrangement is dis- 

 tinctly seen in larger grasses like corn or sorghum. A 

 leaf consists of two parts, the sheath and the blade. The 

 sheath is wrapped around the stem, usually for some 

 distance above the node. It is usually split on the side 

 opposite the blade, one side of the sheath overlapping the 

 other. The blade, commonly called the "leaf," is 

 attached at the upper end of the sheath; it is usually 

 narrow, flat, and gradually pointed. A strong vein or 

 vascular bundle passes along the center from base to 

 apex, and on each side parallel to the mid- vein, are 

 several delicate lateral veins. These veins are also 

 known as nerves. They consist of minute tubes for the 

 conduction of sap from the stem into the leaves. By 

 holding a thin blade up to a strong light, numerous 

 minute cross veins may be seen. At the base of the 

 blade where it joins with the sheath is a delicate mem- 

 brane running up around the stem for a short distance. 

 This is called the ligule. It is usually less than one-half 

 inch long, often much shorter, sometimes so short as to 

 be detected only with a lens. 



