The structure has been defined by the work of several authors; the d-, l- and dl-forms are known; the d-form
is found in the essential oils of Mentha silvestris, Cymbopogon sennaarensis and Japanese peppermint oil; the dl-form is found in
the essential oils of Andropogon iwarancusa, Mentha pulegium var. hirsuta and in mixture with the l-form, Eucalyptus dives; the
l-form, the most abundant, is found in about 30 varieties of eucalyptus and in other plants. It is also reported found in lemon and lime
peel oil, lime juice, other citrus peel oils, black currants, raspberry, celery seed, cinnamon bark, peppermint oil, corn mint oil, other
Mentha oils, nutmeg, pepper, mace, parsley seed oil, rose apple, starfruit, tamarind, elder flower, rosemary, buchu oil, lemon balm,
sweet grass oil, eucalyptus oil and mastic gum fruit and leaf oil.
