IMO

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Note added at 19 mins (2015-12-18 17:51:58 GMT)
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Role of Bitters in Plants
In the case of bitters, it isn’t enough for a plant to be deadly poisonous if it still tastes good to an herbivore. The animal may die but only after the plant has already been devoured. The role of poison in the plant is much more effective if the plant also has a bitter taste and is unpalatable to the animal. This means the bitter flavor of a plant is a signal to the animal the plant may be poisonous and, ideally, should not be eaten.
http://www.theforagerspath.com/the-role-of-digestive-bitters...

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Note added at 26 mins (2015-12-18 17:59:22 GMT)
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The lemon balm leaf is also rich in other biologically active substances, such as tannins, bitters, flavonoids, phenolic acids, chlorophyll and carotenoids, triterpene compounds as well as mineral compounds.
Liść melisy jest zasobny także w inne substancje biologicznie aktywne, takie jak garbniki, gorycze, flawonoidy, kwasy fenolowe, chlorofil i karotenoidy, związki triterpenowe oraz związki mineralne.
http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd...