GRASSES OF IOWA. 



17 



are greatly developed, penetrating the soil in all directions, 

 forming a sward that is exceedingly difficult to break. 



Grass stems are usually round or cylindricil, rarely 

 flattened, and generally hollow between the joints or nodes 

 (solid or with pith in the Andropogons, Indian corn, sorghum 

 and a few other grasses). The nodes, familiarly termed the 

 joints, are the points on the culm or its branches from which the 



Fig. 11. Rhizomes. 1. Rootstock of slough-grass (Sparti/ia cynosuroides). 2. Quack- 

 grass (Agropyon repens). (King.) 



leaves originate; they are usually somewhat swollen, the enlarge- 

 ment being either in the culm or, as is very often the case, in 

 the basal part of the leaf-sheath. The space between two 

 nodes is the interaode. All branches, excepting those of the 

 generil inflorescence, originate in the leaf-axils, that is, 

 within and at the base of the leaf-sheaths, and between the 

 branch and the main axis or stem there always is a longer or 

 shorter twj-keeled prophyllm with its back tnruned towards 



