|The structural units of a higher plant consist of a node,|
an internode, and one ore more buds and leaves at the
node. These units can be repeated indefinitely to form
a shoot, or modified in various ways to alter the
architecture of the plant.
Internodes are essentially the sections of stem between nodes. Ho humm - end of story. Not quite! The internode in fact is a dynamic part the plant, the part responsible for most actual growth in height. You can see the lengthening of internodes most dramatically in vines, which are adapted to extend themselves as rapidly upward as possible to reach the light zone. In vines, cell division and expansion continue in the internodes well below the tip, propelling several sets of expanding leaves ahead of them. Once reaching the light zone, internodes will end growth sooner, resulting in a bushier crown suitable for gathering light. Tree saplings also show dramatic internode elongation in the shade, and many more humble plants will send their flowers rapidly upward by means of strikingly elongate flower stalks.
Internodes are quite distinct in most trees and shrubs (left), but are extraordinarily
elongate in vines like the Clematis (right).
|The bamboo's elongate internodes are the secrets to its |
|Bamboo shoots contain all the|
nodes of a full stem packed close
together. Expansion of all the
simultaneously, results in very
Bamboos are grasses evolutionarily adapted to compete with trees, and they do so with the most extraordinary internodal elongation of all. Each bamboo shoot begins as a compact bud, the "bamboo shoot" of culinary commerce. Within that massive bud, the nodes and internodes for the entire shoot (culm) are preformed, but the internodes are extremely short. When growing conditions are right, the entire bamboo shoot elongates through simultaneous elongation of all of its internodes, reaching full height in a matter of days. The legendary "Chinese bamboo torture" consisted of strapping a prisoner over a bamboo shoot just beginning its expansion phase. The sharp point of the shoot tip pressing against the back quickly became horribly painful.
|This Pachypodium, in the Apocynaceae, |
has virtually no internodes, but grows
slowly through the accumulation of
tissues at the base of each leaf.
|This Neoregelia in the Bromeliad, forms a concise rosette|
|This tiny Drosera rosette is dwarfed by its much larger flowers. The flower|
stalks consist of greatly elongate internodes, in contrast to the virtual lack
of internodes within the rosette of leaves.
|The stalk of the Egyptian papyrus plant|
(Cyperus papyrus) is a single elongate
internode. The tassle at the top consists
of several dozen nodes packed closely
together through lack of any internode
|Gaillardia daisies are normally compact rosettes, but|
under the influence of gibberellins can stretch out via
Internodes are therefore the unsung heroes of plant growth. They determine whether a plant will be a skinny, stretched-out vine, a squat mound of leaves, or something in-between.