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.