Indonesia produced 60 %, Grenada 40 % of the 5600 tons of nutmeg (the dry shelled seeds) and 1400 tons of mace (the dry arillus) of the tropical rain forest tree Myristica fragrans. Restriction of male flowering trees to 10 % and spacing at 9 metres would rise yields per ha sharply above the usual 800 kg nutmeg and 160 kg mace, at 2000 fruits per female tree.In Grenada air-layering and approach-grafting, although expensive, were developed for practical use. In New Guinea the tree showed a 1:1 segregation into a female-only flowering sex, with strong correlation between production and stem girth, and a male-flowering sex, mostly bearing also female flowers and fruits.Investigations for a visible chromosomal sex mechanism showed 44 (2n) nearly isodiametric chromosomes (0.4-1.0μ) and 'non-localized' centromeres. Breakage of chromosomes by X-rays produced persisten fragments, proving nutmeg to be the first dicotyledon with diffuse centromeres.The hypothesis was developed that nutmeg had four pairs of sex chromosomes. The heterogametic female had four facultative nucleolar sex chromosomes, in meiosis orientated by the nucleolus. The variation in female flowering was explained by partial failure of orientation. If proved, the hypothesis offered opssibilities for sexing young seedlings and improvement by breeding.
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