In Archaeocalamites, which certainly deserves generic rank, the branches may occur on every node, but only in certain parts of the stem; the ribs of successive internodes do not alternate, but are continuous, indicating that the leaves were superposed.
The same order of events may be ascertained to take place in the stem; but in this region it is complicated by the occurrence of nodes and internodes, growth in length being confined to the latter, many of which may be growing simultaneously.
It may be due to insufficient illumination (Etiolation), as seen in geraniums kept in too shaded a situation, and is then accompanied by soft tissues, elongation of internodes, leaves usually reduced in size, &c. The laying of wheat is a particular case.
The numerous cultivated varieties are distinguished mainly by the colour of the internodes, whether yellow, red or purple, or striped, and by the height.
If this arrangement is expressed by a fraction, the numerator of which indicates the number of turns, and the denominator the number of internodes in the spiral cycle, the fraction will be found to represent the angle of divergence of the consecutive leaves on the axis.
In cases where the internodes are very short and the leaves are closely applied to each other, as in the house-leek, it is difficult to trace the generating spiral.
Long creeping or subterranean rhizomes, with elongated internodes and sheathing scales; the widely-creeping, slender rhizomes in Marram-grass (Psamma), Agropyrum junceum, Ely7nus arenarius, and other sand-loving plants render them useful as sand-binders.
The nodes are solid, a strong plate of tissue passing across the stem, but the internodes are commonly hollow, although examples of completely solid stems are not uncommon (e.g.
The internodes continue to grow in length, especially the upper ones, for some time; the increase takes place in a zone at the extreme base, just above the node.
A few of the lower internodes may become enlarged and subglobular, forming nutriment-stores, and grasses so characterized are termed " bulbous " (Arrhenatherum, Poa bulbosa, &c.).
In internal structure grass-culms, save in being hollow, conform to that usual in monocotyledons; the vascular bundles run parallel in the internodes, but a horizontal interlacement occurs at the nodes.
When more than one-flowered, distinct internodes are developed between the flowers.
Each double leaf-trace passes through four internodes before becoming a part of the stele; the double nature of the trace is a characteristic feature.
Long and short shoots occur also in Cedrus and Larix, but in these genera the spurs are longer and stouter, and are not shed with the leaves; this kind of short shoot, by accelerated apical growth, often passes into the condition of a long shoot on which the leaves are scattered and separated by comparatively long internodes, instead of being crowded into tufts such as are borne on the ends of the spurs.
The finer branches are green, and bear a close resemblance to the stems of Equisetum and to the slender twigs of Casuarina; the surface of the long internodes is marked by fine longitudinal ribs, and at the nodes are borne pairs of inconspicuous scale-leaves.
The trabeculae are united together by these thickened internodes, and the result is a fenestrated septum, which in older septa may become solid and aporose by continual deposit of calcite in the fenestrae.
The internodes are elongated and hollow.
An Equisetaceous plant, which Brongniart named Phyllotheca in 1828, is another member of the same flora; this type bears a close resemblance to Equisetum in the long internodes and the whorled leaves encircling the nodes, but differs in the looser leaf-sheaths and in the long spreading filiform leaf-segments, as also in the structure of the cones.
Using Calamites as a generic name for all those Calamarian stems in which the ribs alternate at the nodes, we have, on Weiss's system, the following sub-genera: Stylocalamites, branches rare and irregularly arranged; Calamitina, branches in regular verticils, limited to certain nodes, which surmount specially short internodes; Eucalamites, branches present on every node.
The axis is usually very much contracted, no internodes being developed, and the portion bearing the floral leaves, termed the thalamus or torus, frequently expands into a conical, flattened or hollowed expansion; at other times, though rarely, the internodes are developed and it is elongated.
In some species branches of the rhizome with tuberous internodes are formed, which serve as a means of vegetative reproduction.
A, Longitudinal section of the rhizome, including a node and portions of the adjoining internodes; k, septum between the two internodal cavities, hh; gg, vascular bundles; 1, vallecular canal; s, leaf-sheath.