Some Relationships Between Leaf Structure and Resistance to Insects of Elms

摘要

The leaf appendages and structures of four elm species and eight clones of U. pumila were studied by means of a scanning electron microscope and paraffin-micro-ton-sectioning. At the same time, the resistances of these species and clones against the elm leaf beetle, Pyrrballa aenescens, were determined by investigation in the test plantation. According to the percentage of the eaten leaf area, all species and clones were classified into two types, resistant trees and susceptible trees. The observation and analysis of leaf appendages and structures gave some indications that the resistant trees seemed to be more heavily waxed on the adaxial surface than susceptible trees. Trichomes of elms can be classified as glandular hairs, and covering hairs, andthe density of covering hairs and thickness of the cuticle on the adaxial surface were negatively correlated to the percentage of eaten leaf area (r=—0. 719 and — 0. 889 respectively). A multiple regression was made and showed that the density of covering hairs (X_1)and the thickness of cu-ticle(X2) affected the percentage of eaten leaf area (Y) greatly (Y=35. 87 — 7. 76X_1 — 255. 74X_2, r_(y.12)=— 0. 925), and that the thickness of cuticle played a more important role in defending against the elmleaf beetle than the density of covering hairs. Compari-son between resistant trees and susceptible trees indicated that the mean density of adaxial surface hairs and the mean thickness of cuticles of resistant trees were 171% and 319% greater than those of susceptible trees respectively. In addition, The resistant trees differed from susceptible trees in that all resistant trees had druse (calcium salts) in their mesophyll cells, and that some of them had two layer hypodermis cells.