想想下次你咬一个脆苹果或喝一杯水时的情景。 您正在目睹一个复杂的内部管道系统的结果，该系统已经默默工作了几个月。 该系统植根于茎。
在植物学中，茎不仅仅是一根简单的棍子，将叶子支撑在阳光下。 它是维管束植物的中轴，从根部伸出来支撑树枝并产生芽，芽发育成枝条和叶。 但它真正的工作是运输。 它容纳了维管组织——木质部和韧皮部——充当植物的循环系统，将水、矿物质和食物输送到生物体的每个角落。
茎的内部结构
Cutting the stem horizontally reveals a structure that promotes efficiency. Most stems have a central core called a pith, a spongy tissue that provides structural support. This core is surrounded by strands or bundles that conduct xylem and phloem. Outside these bundles is the cortex, which in woody plants is the outermost layer forming the bark.
Beneath the bark is cambium. This is the area where cells are actively dividing. It is the engine room of growth, to which new wood and layers of bark are added every year.
“All green stems photosynthesize, as do leaves. In plants such as cacti and asparagus, the stem is the primary site of photosynthesis.”
The distance between the stems has also been considered, as has the lining. Leaves and lateral buds grow at regular intervals called nodes. A stem extension between two nodes is 节间. This ranking is not random. Maximize light and minimize shadows between leaves.
Coping strategies: Beyond basic survival
Not all stems look like tree trunks. In flowering plants, evolution has adapted the basic stem structure to allow plants to survive dormancy, store large amounts of food, and reproduce asexually. These customizations are so unique that they have their own names.
- Rhizome: A horizontal underground stem that allows plants such as ginger or bamboo to establish themselves in new land.
- 鳞茎: A short, upright, swollen underground stem that stores food for the plant during difficult seasons.
- Tuber: A modified stem of a starch-storing plant. A classic example is the potato, whose “eyes” are actually nodes that can sprout into new plants.
- Bulb: A short stem surrounded by bulbous fleshy leaves designed to protect the plant during dormancy.
- Stolon: A horizontal stem that grows above the ground and occasionally sends up new plants. Strawberries use this method to expand their territory.
These changes allow the plants to survive the winter, tolerate drought and spread without seeds. These are essentially backup plans written into the 植物的DNA.
绿色引擎
我们通常认为叶子是植物中唯一制造食物的部分。 这仅适用于大多数植物。 所有绿色茎都进行光合作用。 茎外层的叶绿素就像叶子一样捕捉阳光。
在某些环境中，叶子是一种负担。 仙人掌生活在沙漠中，通过叶子失去水分就等于被判了死刑
