Botany lectures Last lecture Biology department stage first

� Botany lectures � Last lecture � Biology department / stage : first grade � 2020

� The stems � The main function of stems are to � 1/ support the leaves � 2/ to conduct water and minerals to the leaves to use it in photosynthesis � 3/to transport the products of photosynthesis from leaves to other parts of plant.

Plants divides into 1 - monocots(have one seed inside the seed coat) 2 - dicots( have two seed inside the seedcoat). �

MONOCOTS DICOTS Seed with one cotyledon (seed leaf). Flower parts in threes or multiples of three. Leaf with more or less parallel primary veins Vascular cambium and cork cambium absent Vascular bundles of stem scattered Pollen grains mostly with one aperture Seed with two cotyledons (seed leaves. Flower parts mostly in fours or fives or multiples of four or five Leaf with a distinct network of primary veins Vascular cambium, and frequently cork cambium, present Vascular bundles of stem in a ring Pollen grains mostly with three apertures (thin areas in the aperture wall—see Figures 23. 6 and 23. 7)

� Monocotyledonous Stems Most monocots (e. g. , grasses, lilies) are � herbaceous plants that do not attain great size. The stems have neither a vascular cambium nor a cork cambium and thus produce no secondary vascular tissues or cork.

As in herbaceous dicots, the surfaces of the stems are covered by an epidermis, but the xylem and phloem tissues produced by the procambium appear in cross section as discrete vascular bundles �

scattered throughout the stem instead of � being arranged in a ring (Fig. 6. 12). Each bundle, regardless of its specific location, is oriented so that its xylem is closer to the center of the stem and its phloem is closer to the surface.

In a typical monocot such as corn, a bundle’s xylem usually contains two large vessels with several small vessels between them . �

� Dicot stems: � Typical dicot stem show following � characters: 1/ presence of well- defined epidermis � with cuticle. 2/cortex has collenchyma tissue as a layer under the epidermis or as discontinuous patches. 3/ vascular bundles are open model and � arranged in a ring surrounding pith. 4/ the center of pith is formed from of � parenchyma tissue. �

SPECIALIZED STEMS � Rhizomes : are horizontal stems that grow below � ground, often near the surface of the soil. ( as in iris ). 2. Tubers � Tubers are enlarged stem structures used as � storage organs for nutrients (as in potato). 3. Bulbs � Bulbs is modified stems underground represent � the resting stage of certain seed plants(as in onion). � 4. Cladophylls � They are green cylindrical or flattened leaf-like branch of limited growth ( as in Asparagus). � �

The leaves � Leaves are the flat green part that grow from a plant � stem and that function mainly in making food by photosynthesis. Parts of leaf: � 1 -leaf base: this is the part were a leaf attaches to � the stem, leaf base has two small leaf-like structure called stipules. 2 -petiole: is the long, thin stalk that links the leaf � blade to the stem. � 3 -lamina: also known as leaf blade, its green, flat � surface. It consists of a small branched vein and veinlets.

Leaf

� Types of leaves: � A/ Simple leaf: when a single blade is � connected to the main stem by a petiole(ex: cucumber leaf). B/ Compound leaf: is a leaf made up of � two or more leaflets, her the midrib of the leaf is branched into different leaflets and is connected by a single petiole( ex: palm leaves).

Venation of leaves:

1 -reticulate venation: the veinlets are � randomly arranged and form a complex network of veinlets (ex: dicotyledon plants like Rose plant). 2 -parallel venation: the veinlets run parallel to each other. (ex: monocotyledon plants like Cana indica plant). �

leaf venation

� Phyllotaxy of leaves: is the pattern of � arrangement of leaves on the stem. 1 -alternate: a single leaf develops at each � node on stem alternatively. 2 -opposite: a pair of leaves develops at � each node opposite to each other. 3 -whorled: more than two leaves develop � at each nodes to form a whorl of leaves.

� � � � SPECIALIZED LEAVES Shade Leaves because leaves in the shade receive less total light needed for photosynthesis, they tend to be larger than their counterparts in the sun. In addition, since they receive less intense sunlight and heat, they are thinner, and have fewer well-defined mesophyll layers and fewer chloroplasts. They also do not have as many hairs. Tendrils There are many plants whose leaves are partly or completely modified as tendrils. These modified leaves, when curled tightly around more rigid objects, help the plant in climbing or in supporting weak stems.

� � � Spines and Thorns The leaves of many cacti and other desert plants are modified as spines. This reduction in leaf surface correspondingly reduces water loss from the plants, and the spines also tend to protect the plants from browsing animals. In such desert plants, photosynthesis, which would otherwise take place in leaves, occurs in the green stems. Storage Leaves Desert plants may have succulent leaves (i. e. , leaves that are modified for water retention). The adaptations for water storage involve large, thin-walled parenchyma cells.

� � � � The flower: is the part of a plant which is often brightly colored, grows at the end of a stem, it represent the reproductive organ in plant, and it survive only for a short time. Flower parts: 1 -peduncle: this is the stalk of the flower. 2 -receptacle: the part of the flower to which stalk is attached to, its small and found at the center of the base of the flower. 3 -sepals: small, leaf-like parts growing at the base of the petals, they form outer layer that protect the flower, generally they green colored, and collectively they called calyx.

� 4 -petals: it lies above the sepals, often bright colored, their main function is to attract pollinators such as insects, the petals are collectively known as the corolla. � 5 -stamens: these are male parts of a flower. Many stamens collectively called Androcium, they are structurally divided into two parts: � 1/filament 2/ anthers � 6 -pistil: this form the female parts of a flower. A collection of pistils is called the Gynoecium. � **Pistil consists of four parts: 1 -stigma 2 -style 3 -ovary 4 -ovules �

� The fruit � Fruit is the ripened ovary, � together with seeds, of a flowering plant. Parts of fruit: � 1/ epicarp: the outer layer � 2/ mesocarp: middle layer, � fleshy, edible poetion of fruit. 3/endocarp: inner layer, rough portion where the seeds is accommodated. �

Types of fruits: � 1 -simple: one fruit has developed from the ovary of a single flower (ex: fleshy like tomato, dry like coconut). 2 -aggregate: a fruit formed from several ovaries of � one flower that produces many tiny fruits clustered tightly together (ex: strawberry). 3 -multiple: a fruit formed from the fusion of the � ovaries of many different flowers which develop closely together to form one bigger fruit ( ex: pineapple, figs). � �