3Leaf TissuesA leaf is considered a plant organ and typically consists of the following tissues:An epidermis that covers the upper and lower surfacesAn interior parenchyma called the mesophyllAn arrangement of veins (the vascular tissue).
4EpidermisThe epidermis is the outer one- or multi-layered group of cells covering the leaf. The epidermis has several functions: - protection against water loss (a vaxy cuticle) - regulation of gas and water vapor exchange (stomata) - secretion of metabolic compounds - absorption of water (in some species) .A multi-layered epidermis4
5Mesophyllmeans "middle of the leaf", i.e. the tissues of a leaf that are located in between the layers of epidermis and carry on photosynthesis.The mesophyll of the leaf consists of parenchyma tissue. Since the mesophyll cells contain chloroplasts the tissue is also referred to as chlorenchyma .Chlorenchyma cell5
6Functions of the Mesophyll In most dicot leaves the mesophyll is differentiated into palisade parenchyma (A) and spongy parenchyma (B).The palisade cells are responsible for photosynthesis because they contain chloroplasts.The spongy mesophyll, together with the intercellular air spaces, allow for the interchange of gases6
7Vascular Tissue Vascular tissue is a complex tissue. The primary components of vascular tissue are the xylem and phloem. These two tissues transport fluid and nutrients.Vascular tissue is organized into discrete strands called vascular bundles.
8Cross Section of Papyrus Leaf e epidermisbb bulliform cells (they cause the leaf to roll up in response to low water availability )skl sclerenchymacs vascular bundle8
9Clivia leaf cross section silná kutikula, ztlustlá epidermis The epidermis has a thick cuticle.9
10European Yew (Taxus baccata) Cross Section of a Needle X – xylemf - phloemskl – sclerenchymae – epidermisku – cuticleka – cambiumpp – palisade parenchymahp – spongy parenchyma10
11Rubber fig (Ficus elastica) Cross Section of a Leaf pp - palisade parenchyma hp - spongy parenchymae - epidermis ku - cuticle cs - vascular bundle st - stoma11