leaf arrangement

leaf arrangement e - the order of placement of leaves on the axis of the shoot (Fig. 26). May be:

Leaf classification

Distinguish between simple and compound leaves. Leaves that have one plate (solid or notched) are called simple. Simple leaves at

l

Rice. 27. Compound Leaves:

1 - ternary; 2 - palmate; 3 - unpaired pinnate; 4 - paired pinnate.

istopades fall off completely or do not fall off at all (in most herbaceous plants). Such leaves are characteristic of the vast majority of plants (birch, maple, dandelion).

compound leaves- - leaves, consisting of several clearly separated leaf blades (leaflets), each of which is attached to a common petiole (rachis) with its petiole. Often a complex leaf falls off in parts: first the leaves, and then the petiole.

Depending on the location of the leaves, they distinguish (Fig. 27):

Pinnate leaves - leaves in which leaflets are located on the sides of the rachis. When the top of the rachis ends with one unpaired leaflet, such leaves are called pinnate(rosehip, white acacia). At parapinnate leaf, all the leaves have a pair (peas, yellow acacia).

Palmately complex leaves - leaves in which leaflets are not located along the length of the rachis, but only on its top in one plane (chestnut, lupine).

A special case of a complex leaf is trifoliate leaf - a leaf that has only three leaves (clover, sour).

The rachis of compound leaves can form lateral branches, then double-, thrice-four-pinnate leaves appear. For example, mimosa has a double-pinnate leaf.

Leaf venation

Venation- this is a system of conducting bundles in leaf blades.

Rice. 28. Leaf venation:

1 - parallel; 2 - arc; 3 - reticulate with a pinnate arrangement of the main veins; 4 - reticulate with a palmate arrangement of the main veins; 5 - dichotomous.

The nature of the arrangement of the veins and the shape of the leaf blades are closely related (Fig. 28). Distinguish:

simple venation- only one vein (mosses, club mosses) penetrates the leaf blade from the base to the top;

dichotomous venation- the leaf blade is pierced by forked branched veins (ginkgo);

arc venation- the leaf blade from the base to the top is pierced by several identical veins arranged in an arcuate manner (lily of the valley, hellebore);

parallel venation- the leaf blade from the base to the top is pierced by several identical veins, located strictly parallel (rye, sedge);

net venation- usually one vein enters the leaf blade from the petiole, which then gives branches - lateral veins, forming a dense network. Reticulate venation can be pinnate and palmate.