Studies on stem structure of x Laburnocytisus adamii (poit) scheid.

摘要

A study was conducted to compare the stem structure of shoots associated with three different types of flowers found in Laburnocytisus adamii and see whether the Laburnum-type and Cytisus-type differed in stem structure from Laburnum vossii [Laburnum watereri] and Cytisus purpureus, respectively. Shoots were selected from the Laburnocytisus adamii tree growing in the Treborth Botanic Garden (UK) having leaf and flower types characteristic of Laburnum, Cytisus and Laburnocytisus. Shoots were also selected from plants of Cytisus purpureus and Laburnum vossii. Samples were washed, cut, stained, examined and photographed with transmitted light microscope. In all stem types, vessels appeared similar in structure: round in transverse section, thick-walled and well pitted. In all types, the bordered pits were alternate and round, oval or slightly elongated. Spiral thickening was present in some vessels. Rays were possibly wider in Laburnum than in Cytisus-type. In all stem types, ray cells were rounded in tangential longitudinal section. In radial longitudinal section of all stem types, the ray cells had thick, well-pitted walls. Rays were heterogeneous but there appeared to be a higher proportion of procumbent cells in Laburnum-type and Laburnum vossii, compared to Cytisus-type, which had more upright cells. The main differences between the three shoot types on Laburnocytisus adamii were: (1) presence of hairs on young shoots in Laburnum- but not Cytisus-type and presence of bark ridges with longer persisting epidermis in Cytisus- than Laburnum-type; (2) crescent-shaped caps of gelatinous fibres in the cortex of Laburnum-type and Laburnocytisus-type; less obvious in Cytisus-type; (3) stone cells in groups in Laburnum-type; present as isolated cells in Cytisus-type and Laburnocytisus-type; (4) rays heterogeneous in all specimens, but there appeared to be more procumbent than square or upright cells in Laburnum-type compared with more square and upright cells than procumbent in Cytisus-type. In all these features, the Laburnum-type stems appeared identical to those of Laburnum vossii, and the Cytisus-type stems were indistinguishable from those of Cytisus purpureus. The Laburnocytisus-type stems appeared to be intermediate, veering towards the Laburnum-type in having crescent-shaped caps of gelatinous fibres, but towards the Cytisus-type in frequency of stone cells.