MORPHOLOGY OF THE VEGETATIVE ORGANS 99 



The nodes are capable of growth after the maturity 

 of the internodes. By virtue of this character the culm is 

 able to change its direction by bending at the nodes, the 

 latter increasing in length on the outer side. This tendency 

 may be observed in decumbent culms, the terminal por- 

 tion remaining erect while the basal portion may become 

 prostrate. In such cases the nodes first elongate on the 

 under side and later on the upper side as the successive 

 internodes become horizontal. The node is usually indi- 

 cated externally by a more or less well-marked zone 

 showing a difference in color, texture or pubescence. The 

 swelling often present near the node is a part of the 

 sheath and will be described in connection with that 

 organ. 



In young shoots, the leaves grow at first much faster 

 than the internodes, so that the terminal portion or bud 

 consists of several sheaths fairly well developed, one within 

 the other, while the corresponding internodes are very 

 short. Later these internodes elongate rapidly, separating 

 the leaves. By this means the youngest portion of the 

 shoot is always well protected by the surrounding 

 sheaths. 



The culms are usually cylindrical or nearly so, but may 

 be distinctly flattened. They are never 3-angled as in 

 sedges. The mature culm in proportion to its weight has 

 great strength, especially to resist bending. This condi- 

 tion is aided by the tubular shape and by the hard tissue 

 of the walls. In addition to the sclerenchyma fibers, so 

 abundantly produced as to form a solid ring of tissue with 

 the vascular bundles, there is usually deposited a con- 

 siderable quantity of silica. 



124. Duration. The culms of most grasses are herba- 

 ceous and die down at least to the surface of the soil. In 



