Macadamia nut

See: Macadamia spp. Macadamia spp.

There are three cultivated species of macadamia nuts. They all originate in Northern Australia but are now cultivated in Hawaii and California also. The species are of doubtful taxonomic rank, and they interbreed freely to produce fertile hybrids. Some scope for local amateur breeders . Mace

See: Myristica fragrans. Macro-evolution

Evolution above the species level, as opposed to microevolution, which is evolution below the species level. Macro-evolution operates during periods of geological time, it produces changes that are new, it produces an increase in complexity, it is irreversible, it produces new species, and it produces new genetic code. Micro-evolution is the exact converse in all of these attributes.

It is now thought that the mechanism of macro-evolution is natural selection operating on emergent properties, at all systems levels. Macroscopic

Visible to the naked eye, c.f. microscopic. Magnesium

An essential plant nutrient. Magnesium is a mobile element and, consequently, the older leaves show symptoms first. Deficiency is easily recognised by a necrotic area between the main veins of the older leaves. It can be cured by an application magnesium sulphate (bath salts). Maize

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