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Investigative study of angiosperms morphology [On plant stems] Bij Javia Preface The following project is an investigative project on angiosperms morphology where we were required to analyze characteristics of stems and understand the modifications of the same. Acknowledgement I would like to thank many people who have contributed to the completion of this project. My biology teachers have especially helped me by providing guidelines and giving helpful tips on how to go about the project. Many others have also helped me in collecting the pictures. I sincerely thank them all. Angiosperms Angiosperms, also known as angiospermae are the most diverse group of land plants. Though they are seed producing plants like gymnosperms, angiosperms produced enclosed seeds. These are flowering plants and produce fruits containing seeds. Some prominent characteristics of angiosperms are : flowers, which are the reproductive organs of the plant and also most distinguishing feature; stamens as the female reproductive organ; anther, the male reproductive part, producing smaller pollen grain which aids in easy dispersal; and endospermic seeds. The body of angiosperms can be divided into two fundamental parts: Root system and Shoot system The root system grows downwards into the soil and anchors the plant. It also absorbs water and essential minerals from the soil. On the other hand the shoot system comprising of the stem and the leaves grow upwards. It helps in synthesis of food and its translocation to various parts of the plant. The root system: The root is the non green descending axis of the plant that normally grows downwards into the soil. It develops from the radical and is the first structure that comes out from the germinating seed. It is positively geotropic. The shoot system: The shoot is generally an above ground, aerial, erect, ascending axis of the plant body which develops from the plumule of the embryo. It is usually positively phototropic. It is differentiated into nodes, internodes and bears leaves, branches and flowers. Monocot plant Inflorescence Node e Leaf blade Internode Leaf sheath Picture taken from internet Common name: rice Scientific name: Oryza sativa Family: Poaceae Dicot Plant Picture taken from internet Common name: tomato Scientific name: Solanum lycopersicum Family name: Solanaceae Monocot vs. Dicot Stems Stems develop from the plumule of the embryo of a germinating seed. The stem bears nodes and internodes. The regions of stem where the leaves are borne are called nodes and the portions between two nodes are called internodes. Stem shows negatively geotropic growth. Characteristics of plant stems The stem is the ascending portion o the plant and is the direct prolongation of the plumule. The young stem is green and carries out photosynthesis It bears both vegetative and floral buds it ends in a terminal bud. It has distinct nodes and internodes. It is positively phototropic Functions of stem: It provides support for the main body of plant It supports leaves in such positions so that they can capture maximum of sunlight and flowers and fruits to maximize pollination and seed dispersal. It is flexible and withstands forces exerted by winds and helps the plant to remain upright. It allows transport of water, sugars and other dissolved substances to various parts of the plant. In some plants stems form the organ where food can be stored. In some plants stems form adventitious roots In plants like cactus, stems form the main photosynthetic organ and also stores water. It is therefore possible for the leaves to be reduced to spines to cut down water loss through transpiration. Forms of stem 1. Erect stem: a.caudex/columnar: it is unbranched, erect, cylindrical, and marked with scars of fallen leaves.Example:-palm palm b.culm: Jointed stem with slid nodes and hollow internodes.Example:-Bamboo (Gramineae) Bamboo c.Deliquescent:Branched stem found in trees like Banyan, Mango, Neem etc. Banyan d.Excurrent: cone shaped tree.Example:-pines 2.Weak stems: a.Triling/Trailor:It is a weak stem that spreads over the surface of the ground without rooting at the nodes.Example:Evolvulus, Tridax Wood sorrel i. Prostate/ procumbent: stem trails on the ground and lie prostate. Example:-Evolvulus and oxalis(wood sorrel) ii. Decumbent: stem trails for some distance and then tends to rise at its apex. Example:Tridax, Portulaca tridax iii. Diffuse: Branches of the stem spread out in all directions on the ground. Example:boerhaavia b.Climbers: Stems which attach themselves to nearby object by means of some special devices like hooks, tendrils, and are known as climbers. Examples: bougainvillea(by hooks), wild pea(by tendrils) Wild pea c. creeping stem/Creepers: These stems grow horizontally on the ground and gives off roots at each node. Modifications of stems: A. Ariel modification: 1. Stem tendrils: it is a slender, spirally coiled, thread like structure which helps the plant to climb. When it comes in contact with the neighboring object it coils round it and thus attaches the plant to the object. Examples: grapes/grapevine, passiflora, gourds (cucumber,pumpkins,watermelon) 2. Stem thorn: It is a hard usually straight and deep seated structure with vascular connections. It functions as an organ of defense. Examples: pomegranate, bougainvillea, Carissa,etc. carissa [prickles and hooks: these develop only from the cortex and epidermis and found at nodes or internodes. They help in climbing. They are exogenous in origin. Example: Rose, Smilax ] 3.Phylloclade: the stem is modified into a flat, fleshy and green leaf-like structure which has a succession of nodes and internodes. Leaves are modified into spines or scales to check transpiration and the function of photosynthesis is taken up by the stem. They often retain water. Examples: opuntia, euphorbia, etc. opuntia 4.Cladode: This is a green, cylindrical/flattened stem branch of limited growth. However unlike phylloclade these have only a couple of internodes. Leaves are either reduced to scales or modified into spines. B.Sub ariel modification: 1.Runner: in these stems roots develop on the lower side and leaves at the upper side from the nodes. Example: cynodon dactylon(doob grass), oxalis Doob grass 2.Stolon: In it branches develop from the lower part of the main stem and grow for some distance like an arch and finally touch the ground to give rise to new shoot. Example: Fragaria(wild strawberry), Jasmine, Peppermint strawbery 3.Sucker: In it the main stem grows in the soil but branches develop from the nodes and comes out from the soil. Example: mint, Pineapple, Chrysanthemum 4.Offset: Generally these occur in aquatic plants which have fragile stem. Internodesof offset are small and thicker and each node bears a rosette of leaves and a tuft of roots. It is also known as aquatic runner. Example: Eichhornia C.Underground modification: This type of modification generally occurs for food storage and vegetative propogation. 1.Tuber: The tips of branches becomes swollen in the soil. Eyes are found on them which are axillary buds and covered with scaly leaves. Example:Potato ginger potato 2.Rhizome: It is fleshy stem which grows horizontally in the soil. Small nodes and internodes are found on it which are covered by scaly leaves. Example:ginger, turmeric 3.Corm: It is a condensed structure which grow vertically under the soil surface. Example: colocasia, saffron 4.Bulb: Stem is highly reduced and disc like and surrounded by numerous fleshy leaves. Many roots arise from its base. Example: onion, garlic. The fleshy leaves of onion and garlic store food. Conclusion The project has helped me gain practical knowledge of the topics printed in the text books. It has helped me gain better understanding of the features and identifying characteristics of different plant species like for example differentiating a moncot plant from dicot plant. I have also learned about the modifications of the plant stems and how that helps the plant to survive. The shear variety of modification adopted by the plants are amazing and awe inspiring when one understands that this is what that has led t widespread distributions of angiosperms. Bibliography The information has been collected from : Wikipedia ISC biology text book Biology magazines like biology today The images are taken by: Myself From internet Remarks