Annals of Botany 40: 241-250, 1976
© 1976 Annals of Botany Company
RESEARCH-ARTICLE |
The Vascular Pattern of Italian Ryegrass (Lolium multiflorum Lam.)
3. The Leaf Trace System, and Tiller Insertion, in the Adult
School of Plant Biology, University College of North Wales Bangor, Gwynedd, U.K.
Received: 13 January 1975
The leaf trace system in the region of congested internodes at the base of Lolium multiflorum is described.
A typical major trace in a leaf consists of a collateral bundle having a double bundle sheath and incorporating a certain amount of sclerenchyma. As such a leaf trace is followed down into the stem it increases in diameter, loses the inner (mestome) bundle sheath, and the xylem becomes associated with xylem transfer cells. Lower down, the bundle diameter is reduced although now it has become amphivasal. The internal xylem only is still associated with transfer cells. The proximal portions of the bundle are much reduced, transfer cells, mestome sheath, and sclerenchyma are lacking and the now insignificant bundle merges with a lower leaf trace or some other vascular tissue. Such a bundle in the stem may be in direct contact via bridges with other leaf traces, with the nodal plexus, and with the peripheral plexus that surrounds the inner leaf trace system.
In the base of a typical young plant, approximately one-half of all leaf traces, including all the median veins, join bundles from the next oldest leaf. Approximately one-third join the nodal plexus, and the remainder variously join bundles from the same or next but one oldest leaf to join the peripheral plexus.
The differentiation of tiller insertions into the pre-existing main stem system is highly variable. In a very young tiller a number of traces were seen to terminate before the main system was reached suggesting basipetal differentiation. The actual connections made by the tiller traces may occur with any nearby leaf trace, the nodal plexus, or with the peripheral plexus. Later differentiating leaf traces in a tiller join leaf traces of the tiller itself.
Occasional bundles from secondary tillers by-pass the vascular tissue of the primary tiller to join directly with that of the parent plant. Vascular connections between parent and tiller, although very variable, appear to be totally comprehensive from a functional standpoint.