The idea for the p esent book arose from a 3-day seminar which I organized in March 1984 for young research workers in plant physiology. Participants came from several universities of the French-speaking part of Switzerland and speakers from Basel, Mtinchen, Nottingham, Perpignan, Regensburg, Sheffield, Toulouse, Yale, ZUrich ... and Lausannne. The theme of the seminar was chosen from the range of research fields of our Institute. Meanwhile, feeling it was important to bear in mind that some of our hearers were not specialists in the chosen topic, I wished to pro vide a subject that would be...