Philobiblon

p. 49 A mycorrhiza is a root infested with a particular type of generally beneficially fungus … The most widespread and ancient type, although not the most familiar, bears the cumbersome name of vesicular-arbuscular mycorrhiza (VAM)… form no visible external structures, so it is impossible to tell if a plant has the association without microscopic examination of stained roots. VAM are formed by a small group of fungi… can only survive in association with the roots of a plant. Their principal distinction is the size of their spores, which are quite enormous by fungal standards – in one species of Gigaspora they are over half a millimetre across, compared to a typical figure for most fungi of around 1/100th of a mm. … most plants that can form VAM do so nuder natural conditions because the fungus appears to offer a solution to an otherwise sever problem – the acquisition of the essential nutrient phosphorus… occurs in soil as phosphate ions which are so sparingly soluble that they move only very slowly through the soil… normally less than a millimetre through soil in a day … Remarkably, fossils of one of the first land plants Rhynia, about 400 million years old, have fungi associated with their rhizomes that appear almost identical to modern VAM fundgi.

p. 51 The best-known nonVAM mycorrhiza “is the ectomycorrhizal or sheathing mycorrhiza, characteristic of many forest trees, especially the Pinacae (pines, spruces, larchs firs), the Betlaceae (birches, alders) and the Fagacae (oaks, beeches).. almost all are toadstools, members of the Basidiomycetes. Some are well known and distinctive, such as fly agaric which forms a mycorrhiza with birch…. Ectomycorrhizal roots are stubby and often fork dichotomously, giving dense clusters. Each root tip is surrounded by a sheath of tightly woven fungal hyphae and other hyphae radiate away from this int the soil… The fine fungal threads penetrate the soil, picking up the immobile phosphate ions and transporting them back to the sheath. Meanwhile the fungal hyphae beneath the sheath, which are in contact with the root cells, obtain sugar from them to feed the fungal tissues.”

p. 52 It does seem that extomycorrhizal trees are better able to colonize poor soils than VAM trees, and this is probably because the former get more benefit from the more active fungi. Of course there is a cost to this: the ectomycorrhizal tree probably has to give up more of the carbon that it fixes than does the VAM tree so the latter may be at an advantage on better soils.
Another remarkable feature of mycorrhizas that has recently come to light is their ability to link plants together. .. BY labelling trees with radioactive isotopes, it has been found that materials can pass from plant to plant by means of these links… there is intriguing evidence that seedlings establish in swards more readily if they become mycorrhizal than if they remain uninfected… If this turns out to be widespread and important phenomenon t may force us to rethink our view of plant communities: ecologists have in the past tended to view them as dominated by intense competition between plants; it may be there is more cooperation than we thought.”

p. 57 Soil fauna – flatworms, rotifers or wheel animalcules, hairy backs, land nemerteans, eelworms, earthworms, bear animalcules (Tardigrada), woodlice, terrestrial sand-hopppers, mites, spiders, millipedes, centipedes.

pp. 158 Like an unpredictable genie, pesticides have proved to be a somewhat mixed blessing, for their overall effects can seldom be fully predicted. There are few if any pesticides that are completely specific to their target organisms: discrimination between harmful and harmless organisms is rarely adequate.