Symbiosis

It is a mutually beneficial relationship of two organisms. It may be of following types:

• Mycorrhiza: It is the symbiotic association of fungi with roots of higher plants. The fungus absorbs water, salts and protects plants from soil borne pathogens. In return, it gets shelter and nourishment from the host. It is of two types:

• Ectomycorrhiza: In this case fungi occur outside the root of tree. The hyphae penetrate only between the outer cells and replace root hair, e.g., oak, birch pines, etc.
• Endomycorrhiza: In this case the fungi occur internal to the root tissue and their hyphae develop vesicles and arbuscules (fine branched masses) in the cortical cells. Therefore, it is also called VAM or vesicular arbuscular mycorrhiza, e.g., many orchids like Corallorhiza, Neottia, Epipogon, etc.
• Plants with root nodules: N2-fixing bacteria occur in root nodules of legumes, Alnus, Rubus, Casuarina, etc. The bacteria get shelter and food from the plant. In return, they provide the plant with a major portion of nitrogen fixed by them.
• Myrmicophily: It is the symbiotic relationship between ants and some higher plants. The ants obtain food and shelter from the plant. They protect the plant from other animals. Such association is best seen in Acacia sphaerocephala. In this case, the petiole of compound leaf is hollow and functions as ant shelter. Leaflet tips get modified into glands (Belt’s corpuscles), which possess feeding materials.