FLOWERING: ITS CONTROL BY VEGETATIVE GROWTH INHIBITION

On the other hand, evidence has accumulated, especially among fruit-tree growers, indicating that flowering always follows the cessation of vegetative growth. Deciduous trees flower after winter dormancy, citrus trees flower after water stress, sick or badly starved trees in general do flower heavily. In all cases vegetative growth was interrupted severely. If vegetative growth has not been disturbed, trees keep on growing but never flower, like olives or deciduous trees in the tropics. Even tropical trees usually flower after some interference with their regular growth, which is associated with the monsoon season. This means that first vegetative growth has to be disturbed - this disturbance releasing the lock from a genetically built-in flowering program - and only then can the flowering process take place.

In order to test this theory a few means of artificially interfering with vegetative growth were tried. Olive trees were exposed to a limited amount of cold weather which is necessary for flowering, and then the cold effect was reversed. Limitation of root development of citrus and avocado plants caused unsatisfactory supply to the upper parts and resulted in increased flowering. Juvenile peach trees were treated with paclobutrazol, which inhibited growth and forced flowering. Girdling olive and citrus trees caused more flowering on the girdled scaffolds. Girdling also forced juvenile olive trees to start producing flowers and fruits. Finally, Lemna plants grown under non-inductive flowering conditions were forced to flower by using growth inhibitors such as salicylic acid, poisons like KCN and ferricyanide, or even by a high P/N ratio.

This evidence indicates that the suggested hypothesis might possibly be the right approach to an understanding of the flowering phenomenon.

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