Abstract
Very few studies of flower bud in winter bud of pines have been made in spite of their importance for the breeding of pines. For this reason a study was made on development of flower bud in P. densiflora (P. d.) and P. Thunbergii. (P. T.).
Winter buds of both species were sampled from each one tree in Tanasi Nursery in Tokyo, throughout the growing season. (Table 1) They were embedded and sectioned, using standard techniques.
It was found that the general pattern of development is the same in “female, ” “male, ” and “vegetative” buds. Origin of bud was rarely observed in the lower axillaries on the main axis of winter bud of two species during the middle part of July. (Fig. 1, 2.) In the early part of August, origin of bud was recognized in almost all the winter bud. Many bud origin and cataphylls were recognized in all winter buds on the middle part of August. (Fig. 3) (Table 1)
During the first week of September, the primordia of the future male sprophylls were formed in young cone initial of P. d. (Fig. 4.) and the initiation of the female cones lagged about 2 weeks behind the male cones. The initiation of both male and female cones of P. T. was about 10 to 14 days later than P. d.
WAREING described that the initiation of both male and female cones in P. sylvestris appeares when the day length decreased approximately 1 1/4 hours from the summer solstice. Corresponding day length in Tokyo is in the last decade of August. Initiation of male cone in P. d. occurs during this season but the case of P. T. did not fit this pattern.
