According to the late Sir William Bayliss, a leading physiologist, the vitamins, which the plant alone knows how to manufacture, are a kind of chemical messengers (hormones). “They are obtained from the plant, and are particularly abundant in fresh green vegetables and fruit.” … “Their precise mode of action is still unknown, but in their absence normal growth and function is impossible and certain diseases make their appearance.” Hence the normal growth of the animals depends upon stimulations and influences directly derived from the plant kingdom. The evolution of the animal is in large part directed by the plant, which is also saying that it is cosmically directed, in virtue of those terrestrial and solar influences which the plant purveys. But it is also saying, in a most important sense, that all organic evolution is directed by the amount of mutuality existing between the kingdoms and what this involves in bio-sociality. If the vitamins are, in Sir William's words, “obviously a kind of chemical messengers,” then we must consider them as the hormones of symbiosis, as “messengers” of health—the diametric opposites of the alkaloids, the vegetable poisons which are of appalling efficacy in the physiological economy of the animal. By symbiosis I mean not parasitism, not commensalism, but definite, almost deliberate, mutual adaptation for the purpose of mutual service, on the part of living things, nearly always of different orders of creation, broadly, that is, between the plant and the animal (“Norm-symbiosis”).
Electrochemical Detection of Neurotransmitters