Within Annual Ring and Pith-to-bark Variations of the Microfibril Angle in the S2 Layer of Tracheid Walls in 106-year-old Plantation Trees of Japanese Larch

Observations were made of within annual ring and pith-to-bark variations of the microfibril angle of the S2 layer (MF angle) of tracheid walls in 106-year-old plantation trees of Japanese larch (Larix kaempferi Carr.). The MF angle was measured by the iodine method. The MF angle within the annual ring decreased from the beginning to the end region of earlywood, whereas in latewood there was less variation than in earlywood, regardless of cambial age. The decrease in MF angle in earlywood is gradual in rings of younger cambial age, whereas it is abrupt in rings of older cambial age, regardless of the rate of radial growth. The pith-to-bark variations of MF angle were found to be constant in earlywood. On the other hand, the MF angle of latewood decreased abruptly in the younger stage followed by a stable smaller angle in the older stage after the 15th to 30th rings. There was no significant correlation between ring width and MF angle of latewood in mature wood (after the 30th ring).