Interaction of Endogenous and Environmental Periods in Plant Growth

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Abstract
The accumulation of dry weight by tomato (Lycopersicum esculentum ) and peanut (Arachis hypogaea) plants varies with the combined lengths of the alternating light and dark periods, which is called cycle length. The optimal cycle length is not the same at all temperatures. The cycle length which produces optimal growth is 22hours at 23[degree]C, 27-30 hours at 14[degree]C and 20 hours at 30[degree]C. By adjusting the environmental cycle length to the optimal value for each temperature, part of the injury and decrease in growth due to non-optimal temperature can be prevented. In their natural environment plants are exposed to a 24-hour cycle. It has been concluded that peanut and tomato plants possess an endogenous, time-measuring mechanism which is slightly temperature dependent, and that for optimal development the external period must be synchronized with the endogenous period of the plant.