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. i 
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 
