When the pine tree is young, the crown is pyramid-shaped and the branches are mostly wheel-shaped. When the seedlings are unearthed and the cotyledons are unfolded, the primary leaves appear first, which are solitary, spirally arranged, linear and lanceolate, and the leaf margin is toothed. It takes 1 ~ 3 years for primary leaves to function as leaves, and then there are needles, usually 2, 3 or 5 bundles, which are inserted at the top of short branches. Each bundle of needles has a leaf sheath at the base, which falls off or exists early. The position of resin channel in mesophyll tissue is relatively constant in adult plants, which can be divided into three types: exogenous, mesophyll and endogenous.
Extended data
The posture of pine trees is tall and straight, which is very attractive. It is for this reason that pine trees symbolize the indomitable spiritual quality of our Chinese nation.
Pine, plum and bamboo are called "three friends of the old cold" and are often praised by people.
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