Skeleton intervertebral discs. It is not as hard and rigid as bone but is stiffer and less flexible than muscle. Cartilage is composed of specialized cells called chondrocytes that produce a large amount of extracellular matrix composed of Type II collagen (except Fibrocartilage which also contains type I collagen) fibers, abundant ground substance rich in proteoglycan, and elastin fibers. Cartilage is classified in three types, elastic cartilage, hyaline cartilage and fibrocartilage, which differ in the relative amounts of these three main components. Unlike other connective tissues, cartilage does not contain blood vessels. The chondrocytes are supplied by diffusion, helped by the
Mycorrhizal fungi and soil carbon storage a similar line of argument, Langley and Hungate (2003) argued that the abundance of chitin in ectomycorrhizal tissues may reduce decomposition rates of these fungi, under the assumption that chitin is recalcitrant. This possibility was tested and refuted recently. Fernandez and Koide (2012) show that chitin does not decompose more slowly than other chemical compounds in ectomycorrhizal tissues, and that chitin concentrations positively correlated with mycorrhizal biomass decomposition rates, rather than negatively. Mycorrhizal fungi are nutrient rich structures compared to the roots they colonize, and it is possible that mycorrhizal colonization of roots leads to increased rates of root decomposition