作 者 ：ZHANG Quan, HU Yu-Xi, LIN Jin-Xing
期 刊 ：植物分类学报 2001年 1期
Keywords:Thuja occidentalis, Female cone development, Ovule initiation, SEM,
Abstract:
The development of female cone in Thuja occidentalis was investigated by means of SEM
together with conventional sectioning technique. It was observed that the female cone initiation in
T. occidentalis occurred in August by the transition of vegetative apices into seed cone apices in
Beijing. Female cone in T. occidentalis consisted of 4~6 pairs of decussate bracts. Usually, two
or three pairs of the fertile bracts in the middle of the cone subtended eight to twelve ovules. The
first structure observed in the axil of the fertile bract was a broad swelling, on which two ovule pri-
mordia initiated. Furthermore, each ovule primordium differentiated a collar-like integument around
the base of the nucellus, and the integument enclosed nucellus progressively and overgrew the nucel-
lus, forming an ovule with a micropyle. During the ovule initiation, it was further noticed that three
ovule primordia were initiated in each of the axil of lower fertile bracts in half of the female cones
observed. However, only two ovules developed, for the middle primordium aborted in later stages,
which indicated that the female cone of T. occidentalis might be derived from that with more ovules
per bract of the ancestor by reduction of the number of ovule per bract. We also preliminarily inves-
tigated the vascular system development of the cone. There was only a middle trace in the bract of
young cones. After pollination, with the intercalary growth of the bracts, 4 to 8 vascular bundles de-
veloped in the bracts. However, the new-formed vascular bundles did not show inverted orientation,
which was reported as a feature in the cone development of Cupressaceae.