Response to light intensity and day-length of two contrasting flower varieties ofAntirrhinum majusL.

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Abstract
The effects of day-length and light intensity on the growth rate and leaf number of an early (Pink Ice) and a late (Orchid Rocket) flowering variety of Antirrhinum majus L. have been investigated. Growth rate, as determined by plant height or dry-weight increase, was greater for Pink Ice in all instances. When the two varieties were grown under similar conditions, the leaf numbers prior to flowering attained by Orchid Rocket were always greater than those of Pink Ice. With high light intensity the long-day (LD) responses of both varieties were characterized by leaf numbers which were on average 30 leaves less than the numbers found on plants grown in short days (SD) at high light intensity. Pink Ice exhibited this photoperiodic response to LD irrespective of whether the light intensity was high (26,000 lux) or low (6000 lux), whereas the leaf number of Orchid Rocket only declined in LD when the intensity was high. Plants of this variety grown in low light LD had leaf numbers similar to plants maintained in high light SD. The data are discussed in terms of two possible light reactions; a primary photoperiodit reaction promoted by day-length and a secondary reaction which was dependent on light intensity.

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