Yoshida - 1981 - Fundamentals of Rice Crop Science

26 FUNDAMENTALS OF RICE CROP SCIENCE
1.24. The culm, node, and internode
of the rice plant (adapted
from Hoshikawa 1975).
The total number of nodes on the main culm is equal to the number of leaves
developed on the culm plus two, which account for nodes for the coleoptile and
panicle. Thus, if a variety develops 15 leaves on the main culm, it has 17 nodes.
Only a few internodes at the top elongate; the rest are short and thickened into a
solid section. The uppermost internode is the longest, and the internodes decrease
in length as their distance from the plant base decreases. The total of unelongated
internodes accounts for only a few centimeters. An elongated internode is conveniently
considered as one whose length exceeds 5 mm. The number of elongated
internodes (ranging from 3 to 8, averaging around 5) varies with variety and
environment. After heading, the sum of the lengths of elongated internodes
accounts for a large fraction of plant height.
The outer diameter of internodes, about 2–6 mm, varies with internode
position, kind of shoot (main culm or tillers), and environmental conditions.
In cross section (Fig. 1.25), the internode has a large hollow space called the
medullary cavity, whose diameter is the inner diameter of the internode. Many
large vascular bundles are found in the middle portion of the internode tissue. In
addition, many small vascular bundles are located near the epidermis. In the lower
elongated internodes, fourth or fifth from the top, many air spaces may be found
between the vascular bundles (Fig. 1.26).