This is especially important for growth on complex, insoluble polymers such as cellulose, because the enzymes released from hyphae have a limited rate of diffusion. These enzymes create zones of substrate erosion around the hyphae, but the tips can grow continuously out of these nutrient-exhausted zones. For this reason, fungi are the major decomposers of organic matter (see wood decay fungi) and also are efficient in capturing mineral nutrients in mycorrhizal associations. In contrast to hyphae, the fungi that typically grow as yeasts seldom have polymer-degrading enzymes because yeasts cannot extend continuously into new zones of substrate. Instead, they form buds for dispersal in water films - an ideal adaptation for utilising simple, soluble nutrients.