CHAPTER 13

LICHEN SYMBIOSIS

Fig. 13.16. Cross-section of the lichen Xanthoria parietina, showing the zonation of tissues.

Fig. 13.17. Left: tightly packed tissue of the upper cortex of the lichen Peltigera canina. Right: thick-walled, hydrophobic hyphae of the medulla of Peltigera.

Fig. 13.18. Sites of potential nutrient exchange in lichens of the soil crust community of semi-arid desert soils. Left: three green algal cells (labelled a) firmly attached to a hypha in the medulla of the lichen Peltula. The arrowhead shows a hyphal projection into an algal cell. Right: a cyanobacterial lichen (Collema sp., which is one of the gelatinous lichens); fungal pegs are closely associated with depressions in the cyanobacterial cells, which are surrounded by a gelatinous sheath.

Fig. 13.19. Isidia (left) and soredia (right): two methods of vegetative dispersal of lichens.

Fig. 13.20. Part of a thallus of Xanthoria parietina, sectioned through an apothecium. Left: many asci are seen just beneath the upper surface of the apothecium. Right: part of a crushed apothecium, composed of packing hyphae (paraphyses) and asci containing ascospores.

Fig. 13.21. A dried soil crust community of lichens, cyanobacteria and fungal hyphae that form a thin covering which binds the surfaces of semi-arid soils. Such a community would be more than 100 years old and represents a relatively early stage in soil formation.

Fig. 13.22. A small fragment of a desert crust community when remoistened, showing several small lichen thalli (Peltula sp.) and one small cyanobacterial lichen (Collema). Most of the soil surface is covered with filaments of the cyanobacterium Scytonema

Fig. 13.23. Top left: The desert crust lichen, Peltula, which typically grows as a thallus composed of several squamules. Top right: the same lichen seen from below, showing a mass of branched rhizinae that ‘root’ into the desert sand. Bottom left: Part of Fig. 12.22, enlarged to show the mass of cyanobacterial filaments (Scytonema sp.). Bottom right: a single filament of Scytonema encased in a mucilaginous sheath with soil particles.

GO TO IMAGES FROM CHAPTER 14?

OR RETURN TO HOME PAGE