Agriculture Reference
In-Depth Information
and homonomy is blurred. The innermost bud scales have rudimentary leaf blades at
their tips that suggest true bud scales in
Acer
are derived through the evolutionary
modification of laminar tissues (Sakai 1990). Similar correlations between the
degree of bud scale development and leaf emergence patterns can be observed in the
Betulaceae (Kikuzawa 1980, 1982).
The situation is somewhat similar in evergreen broad-leaved tree species, but it
is less clear cut because the timing of shoot growth and bud development is not as
constrained seasonally as in broadleaf deciduous trees. Three types of buds can be
recognized: naked buds lacking scales, hypsophyllary buds covered with soft green
leaf-like hypsophylls, and scaled buds covered by many hard imbricate brown
scales (Nitta and Ohsawa 1998). Buds with well-developed scales are typically
found in canopy tree species such as
Castanopsis cuspidata
,
Quercus acuta
, and
Machilus thunbergii
, and naked and hypsophyllary buds in subcanopy or under-
story species such
Cleyera japonica
,
Eurya japonica
, and
Maesa japonica
. Species
with naked buds do not form winter buds, instead having shoot growth with acro-
petal production of leaves throughout the growing period. Species with hypsophyl-
lary buds have shoot growth during April and June in the warm temperate forests
of Japan, forming a terminal bud at the same time that then has no further morpho-
logical development until budbreak the following March or April. Species with bud
scales have rapid shoot growth in May and June; during this stem elongation
period, the shoot tip has an immature hypsophyllary bud. After the completion of
stem elongation in early summer, a bud protected with many scales gradually devel-
ops through the summer, fall, and winter within this immature hypsophyllary bud
(Fig.
2.5
).
Fig. 2.5
Development of buds from May through October and mature bud condition in December
in two evergreen broad-leaved trees:
Cleyera japonica
(
left
) and
Quercus acuta
(
right
). The
hypsophyllary buds of
Cleyera japonica
are produced in spring within the mother bud but show
no further morphological development until the following spring. In
Quercus acuta
, the hypso-
phyllary bud formed in spring develops into a scaled bud throughout the period until budburst the
next year.
Open bars
, hypsophyllary-bud phase;
closed bar
, scaled-bud phase. (After Nitta and
Ohsawa 1998)
