What are tree leaves?
The tree leaves are lateral, flattened, exogenous plant organ of limited growth; they have definite shapes and arising from the notes of the main stem or that of the branches. In general the tree leaves are green in colour due to the presence of chlorophyll and are the major photosynthetic organs of the tree. The leaves are either or compound in nature. The typical leaf consists of lamina or epipodium, leaf stalk or petiole or mesopodium and the leaf base or hypopodium. The lamina is differentiated into leaf apex, leaf margin and the lamina surface.
The network of vascular tissues in the lamina is called venation. The venations are of two types, that is reticulate and parallel. The tree leaves are arranged in acropetal succession, that is the first formed leaves occupy the lowermost position in the branch, while the last formed ones occupy the uppermost position. The major function of tree leaves includes preparation of food by photosynthesis, loss of excess water vapour by transpiration and gaseous exchange during respiration. They also perform some special functions like storage of food and water, mechanical support, protection, trapping of insects and so more.
So as a definition it can be say that, a leaf is a flat, exogenous, lateral structure of stem, containing chlorophyll pigment and bears a bud in its axil.
Characteristics of tree leaves : –
The main characteristics of tree leaves may be described as follow: –
i) The leaves are flat, in structures of limited growth.
ii) The leaf is usually green in colour and cause of this colouration is due to the presence of chlorophyll.
iii) The vegetative leaves are arising due to modification of the apicalmeristem.
iv) After the germination of seed, the first formed tree leaves arise from the cotyledon and are called Cotyledonary leaves.
v) The Leaves are dorsiventral or isobilateral in nature.
vi) Leaves are differentiated into leaf blade or epipodium, leaf-stalk or mesopodium and the leaf base or hypopodium.
vii) The axillary buds are present at the axil of the vegetative leaves.
viii) Sometimes the tree leaves are without petiole and they are called sessile leaves.
ix) Leaves are lateral, exogenous structures, usually with broad lamina to receive more sunlight.
x) The leaves sometimes reduced to provide protection to the stem.
xi) The tree leaves may be simple or compound in nature, i.e., formed by the aggregation of several leaflets.
xii) Compound leaves may be pinnate (with elongated rachis) or palmate (with a shortened rachis).
xiii) The major functions of the tree leaves include photosynthesis, gaseous exchange and transpiration
xiv) The leaves usually appear in acropetal succession, i.e., the lower leaves nix-first formed, while the upper leaves are later formed.
xv) The leaves are provided with vascular tissues and its arrangement is termed as venation, the monocots have parallel venation, while dicots have reticulate venation.
xvi) The lamina, leaf stalk may be modified to perform specialized functions like storage of food and water.
So, the tree leaves are flattened, green, lateral members of the stem developing from the aerial shoots or branches in acropetal succession from the nodes. The first formed tree leaves are the cotyledonary leaves, while vegetative leaves are formed from prophylls. A typical foliage leaf has three main parts, viz., leaf base or hypopodium, petiole or mesopodium and lamina or epipodium. The leaf base is the region of attachment of the lamina with the main stem, the petiole joins the lamina with the leaf base, it is absent in sessile tree leaves. The lamina serves the major functions of photosynthesis, transpiration and respiration.