Observations placeholder

Seasons of Life – Russell G Foster and Leon Kreitzman

Soya beans were not grown in Minnesota because by the time the plants flowered, the cold weather was setting in and killed them off.  Farmers in Maryland could grow the beans, but they ran into difficulties when they tried to stagger the harvest time so that they could organise their work schedules and use their labour and machinery more effectively.  They tried planting out the crop at 2 week intervals, but irrespective of when they were planted, the plants would all set flowers and need harvesting at more or less the same time.................

[two plant physiologists] Garner and Allard attacked the problem by growing Maryland Mammoth tobacco plants in pots and soya beans in troughs outdoors and at different times of the day they moved the plants into a glorified shed that had a tight fitting door and provided a dark chamber.  The following morning they would put the plants outside alongside the controls and continue until the plants blossomed.  By effectively shortening the daylength, they caused the tobacco to flower three months early and the soya beans five weeks early (Garner and Allard 1920).  It was a simple experiment, but essentially they laid the foundations for the modern, multi-billion dollar horticultural industry, as well as leading to a huge improvement in agriculture..................

A large number of plant activities are regulated by photo-period, including the development of reproductive structures in mosses and in flowering plants; the rate of flower and fruit development; stem elongation in many herbaceous species as well as coniferous and deciduous trees; autumn leaf drop and the formation of winter dormant buds; the development of frost hardiness; the formation of roots on cuttings; the formation of many underground storage organs such as bulbs (onions, tubers and storage roots); runner development (strawberry); the balance of male to female flower parts; and even obscure responses such as the quality and quantity of essential oils produced by jasmine.

Since Garner and Allard's seminal discovery, thousands of papers have been published in the long attempt to understand how plants manage to measure relative day length and use the signal to time their development.  The key problems were how light was detected, how day length was measured and how flowering initiated.