Diancecht, the god of medicine and healing, was intensely jealous of Miach, his son, for Miach had become more exalted then he for his great ability to heal. Diancecht, burning with envy, struck Miach once over the head with a sword, but Miach quickly recovered and healed himself. Diancecht struck Miach a second time, this time with greater force, but Miach healed himself again. The third blow was too much for Miach and wrought his death.
When Diancecht buried his son, three hundred sixty-five herbs sprang forth from the earth above Miach's body -- one herb offering cure for any maladies within each nerve of the body. Airmid, Miach's sister, gathered every herb from the earth and arranged them upon her cloak in the shape of a human body, denoting the properties and uses of each herb... but with one swift kick, Diancecht sent the array of herbs flying and the remnants were strewn, misplaced all about the ground.
The rash action of an envious father destroyed the powerful knowledge of the cure for every illness, thus the chance of immortality was lost forever.
However, in turn, whenever we pluck an herb from the earth, we are holding a bit of the Green Man, and when we apply these sacred herbs to someone who is ill, we are re-uniting the herbs with the god, so he and the entire world are again whole and balanced.
Druids know that there are certain times in which certain types of herbs should be collected. Tree leaves should be collected before Midsummer... Leaves and flowers are supposed to be gathered on dry days when flowers first begin to open and are always dried in the shade, so their colors don't fade. Roots are generally gathered in very early spring or in late fall after the plant has begun to die back. And tree barks are best in the soft inner layer (cambium) of the bark between the sapwood and the dead outer bark...
A Druid does not learn everything alone; from time to time he must consult old women, shamans, gypsies, magicians, wayfarers, and all manner of peasant folk and fandom people, and learn from them... Do not be arrogant when in fact you are helpless, and do not regard yourself as a master at the outset; for no one can achieve mastery without labor. Also, learn from those who are more experienced than you, for who can pretend to know everything? Who can be everywhere and know where all things lie? Therefore travel and explore everything, and whatever comes your way, take it without scorn and do not be ashamed to do so... For nature is so excellent in its gifts that... it better benefit a man to know one herb in the meadow, but to know it thoroughly, than to see the whole meadow without knowing what grows on it.