With one new volume each year, this series keeps scientists and advanced students informed of the latest developments and results in all areas of botany. The present volume includes reviews on structural botany, plant physiology, genetics, taxonomy, and geobotany.

The 50th volume of Progress in Botany appears in new guise. In cooperation with Springer-Verlag we have changed from the less attractive typewriter composition to the direct reproduction of a manuscript which was writ ten by means of a text editing system and produced by a laser printer. We, the editors, should like to take the appearance of Volume 50 as the occasion for a few short remarks. Our younger readers are perhaps not aware that our Book Series was founded in 1931 by Fritz von Wettstein, based on the following thoughts and considerations, aptly formulated by him in the Preface to the first volume. "One of the greatest dangers threatening progress in the science of botany is the absolutely unbelievable growth in volume of the literature. The quality of journals, books and individual works that are daily sent to us makes it impossible for anyone person to maintain a general view of the progress made in botany in all the specialized fields, let alone to find time for results from associated su bjects. For varying reasons, every botanist must find this state of matters insupportable. Let us endeavor, in the general interest, to retain a wide background of knowledge, and not become limited specialists. The vitally necessary connections between the specialized fields can only flourish, or even exist, if the general view of botany as a whole can be maintained."

With one new volume each year, this series keeps scientists and advanced students informed of the latest developments and results in all areas of botany. The present volume includes reviews on plant physiology, genetics, taxonomy and geobotany.