The roots and mycorrhizas of herbaceous woodland plants: II. Structural aspects of morphology.

The morphology of vesicular-arbuscular (VA) mycorrhizas in the roots of five species of herbaceous woodland plants, in which root growth and mycorrhiza formation were quantified in the first part of this study was examined. The root anatomy of these species was also examined in detail, using various staining procedures to observe cell wall structure, especially in the region where mycorrhizal colonization was initiated. The morphology of mycorrhizal colonies within the roots of these species was observed at different stages of development using light microscopy. It was found that modifications of endodermal and exodermal cell-walls could determine the way in which fungi entered the roots. It was also found that properties of the cortex considerably influenced the localization of hyphae and arbuscules within roots. Features of VA mycorrhizas that were probably associated with particular endophytes were also noted. It is considered likely that some aspects of root structure have evolved means of regulating the efficiency of mycorrhizal associations.