PHYTOTRON CULTIVATION OF PINUS SYLVESTRIS (L.) PROVENANCES.
Optimal temperature conditions are proved to include a relatively high day temperature and a night temperature ca 10°C lower than the day temperature: 25–15°C or 20–10°C. No or less difference between day and night temperature gave rise to smaller plants.
The light period giving the tallest plants was for the northern provenance 18 h, for the southern one 16 h. A longer as well as a shorter photoperiod caused earlier ceasing of the height increment (=bud setting) and shorter plants.
The same two provenances have been used to study how the conditions given in the first growth period (1) influence the plant development in the second (11) and the following growth periods.
Some seedlings got 18 h, others 16 h during (1): the same photoperiods were used in (11), but half of the material was shifted to the opposite photoperiod. Determinating for the growth during (11) were the conditions in (1). Favourable conditions during (1) (=18 h for the northern, 16 h for the southern provenance) gave rise to good development in (11) irrespective of the conditions in that very period; unfavourable conditions during (1) caused less good development in (11) even after a change to favourable conditions. Influence from (1) has been proved up to the fourth period.