Abstract
The development of incubated tyloses in earlywood vessels were examined within all the sapwood of Castanea crenata SIEB. et Zucc. Particularly, the elongating stages of incubated tyloses in every annual ring of the sample wood were compared with each other.
Each sample tree was felled in various seasons, and the trunk was cut immediately into 3 cm-thick discs (Table 1, Fig. 1). Large discs were further cut into cubic blocks containing the bark, sapwood, and outer heartwood (Fig. 2a). The incubation discs or blocks were placed in the growth chambers which were sealed up in polyethylene bags containing a small amount of water at the bottoms. The growth chambers were kept in the laboratory maintained at 20℃ or 26℃. The incubation discs or blocks themselves were also moistened at intervals of 2 or 3 days. After a certain incubation time (Tables 2 to 6), one disc or block was taken out from the growth chamber and cut to obtain the observation plane (Fig. 2a). The development of incubated tyloses in the area shown in Fig. 2b was observed with a stereoscopic microscope. Incubated tyloses in sample trees A and B were also observed with SEM and TEM by the ordinary method.
The following (1) to (4) were found in each sample tree (Tables 3 to 6). (1) Incubated tyloses developed similarly in the outermost annual ring. (2) Incubated tyloses within sapwood tended to develop more slowly in the inner part than in the outer part. (3) Incubated tyloses developed most slowly in the transition zone in which natural tyloses were developing (Figs. 3 and 4). (4) Incubated tyloses were fewer and did not develop simultaneously in the inner sapwood (Figs. 3 to 5).
Judging from Tables 3 to 6 and (1) to (3) described above, the development of in- cubated tyloses appears to be dependent on neither the distance nor the number of annual ring from cambium, but significantly on the relative distance (value relative to the width of sapwood) (Figs. 6 and 7). The tendency to develop more slowly with the increase of relative distance is more remarkable in the outer sapwood.
Comparing the development of incubated tyloses in sample trees A, B, D, and E incubated at 20℃, incubated tyloses in the outermost annual rings developed more slowly in dormant season (in sample trees A and E) as well as those in Quercus serrata THUNB. The development of incubated tyloses in the inner sapwood seems to be less dependent on the seasons. The activity of ray parenchyma cell in the inner sapwood may be low and less variable in all the sample trees examined.
