It is sometimes possible to induce forest trees to flower early in life. Betula spp. initiated catkins of both sexes in 8 to 30 months from germination when grown rapidly in a glasshouse, or when the main stems were completely 'ringed'. Thuja plicata D. Don seedlings also responded to ringing and to gibberellic acid treatment, while a cutting from a 7-months-old seedling of the tropical tree Triplochiton scleroxylon K. Schum. flowered a meter above ground level in less than two years.Have these induced trees become mature or have they flowered while still
in the juvenile phase? Evidence is accumulating which suggests that many
forest trees are simply more 'reluctant' to flower during the early
years of life, rather than being incapable of so doing. The results of
several experiments concerned with reproductive and vegetative phase
change are discussed, and the suggestion is made that the Hedera plant
may have provided too rigid a model for juvenility in forest trees.
Unequivocal evidence for the induction of the mature phase generally
requires the appearance of stable modifications within a genotype, which
persist when the treatments causing them are withdrawn.