Organography means the description of various organs of plants and animals. The external features of plant organs like stem, root, leaf, fruits, etc. Stem and root form two regions of the plant axis whereas leaf is a lateral continuation of stem and has a limited growth.
Functionally these parts are quite different. While roots help in anchorage, absorption of water and minerals and storage, stems help in conduction of food materials and water besides providing mechanical strength to the plant. Leaves help in photosynthesis, exchange of gases and transpiration.
The functional differences are mainly due to differences in their internal organization. The internal structures of these parts exhibit variations in cell structure and tissue arrangements. The tissues are arranged in these organs to provide maximum functional efficiency and mechanical strength.