Figure 4.26 A transverse view of cortex cells in frozen roots of white clover (Trifolium repens) colonised by indigenous arbuscular mycorrhizal fungi. In uncolonised cells (UC), the plasma membrane is so closely aligned to the cell wall that it cannot be distinguished and what can be seen inside the cell are dots and lines formed by solutes frozen in the cell vacuole. However, some cells contain the many small hyphae of mature arbuscules (Arb) which have the plasma membrane encasing them and large hyphae are evident occupying most of the intercellular spaces surrounding these cells (arrows). Roots were frozen in liquid nitrogen and viewed using cryo-scanning electron microscopy. (Photograph courtesy M. McCully)