THE GRASS FAMILY 15 



pithy. They may be erect, spreading, or creeping; 

 they may be simple or freely branching. A branch 

 is borne only at a node in the axil of a sheath, that is, 

 between the sheath and the cuhn. It either grows up 

 parallel with the parent cuhn until it emerges from 

 the sheath or the young branch spUts the sheath and 

 grows outward. In manuals of botany these two 

 methods of branching are called intravaginal, that 

 is, inside the vagina (Latin for sheath), and ex- 

 travaginal, outside the sheath. In bunch-grasses, 

 Uke orchard-grass and the wheat-grasses of the 

 West, the branching is intravaginal; in Kentucky 

 blue-grass, quack-grass, and others producing rhi- 

 zomes or stolons, the branching is extravaginal. 

 The branches borne at the middle and upper nodes 

 of a culm are nearly always intravaginal. If they 

 spread from the parent culm they do not burst 

 through the sheath but carry it with them. 



Leaves are always borne at the nodes and are 

 always 2-ranked (see Fig. 1, page 9). In corn and 

 other large grasses the leaves sometimes appear 

 to be all on one side instead of 2-ranked. This is 

 due to a twisting of the culm inside the sheath. 

 Sometimes in large grasses, particularly in sugar- 

 cane and in bamboos, the leaves fall, leaving the culm 

 naked. In relatively few grasses the edges of the 

 sheath are grown together, forming a tube. Some- 

 times the blade of the leaf is not developed. This is 

 always the case in the leaves or scales of rhizomes 

 (Fig. 9), and often in those of stolons and in the 



