The concept of using mathematical models to investigate crop growth and productivity has attracted much attention in recent years. A major reason is that modelling can allow an expert in one area to assess the impact of his ideas in the light of other advances in our understanding of crop performance. Whether or not many of the claims made for or the demands made of models can ever be satisfied, this role as a focus for quantitative definition of crop growth is an important one. One consequence is that the development and appraisal of such models requires the efforts of scientists from a wide range of disciplines. This NATO Advanced Research workshop was designed to bring together such a range of scientists to consider the wheat crop, and assess our understanding of the crop and our ability to model its growth and yield. The ideas and organization behind the workshop involved many people. The U. K. interest in a computer model of wheat growth was instigated by Dr. Joe Landsberg (then of Long Ashton Research Station, but now Director of CSIRO Division of Forest Research), who in 1979 started a modelling exercise as part of a collaborative study of the causes of yield variation in winter wheat, involving four research institutes supported by the Agricultural and Food Research Council. Dr.

Inhalt
Preliminaries.- Perturbations of Linear Systems.- Linear Systems with Slowly Varying Coefficients.- Linear Dissipative and Piecewise Constant Systems.- Nonlinear Systems with Autonomous Linear Parts.- The Aizerman Problem.- Nonlinear Systems with Time-Variant Linear Parts.- Essentially Nonlinear Systems.- The Lur'e Type Systems.- The Aizerman Type Problem for Nonautonomous Systems.- Input - State Stability.- Orbital Stability and Forced Oscillations.- Positive and Nontrivial Steady States.