Metamorphic juices

Another motif flowing through Metamorphoses 14 is juice, which appears seven times. Ovid's word is sucus, which has the primary sense of the juice of a fruit, or sap of a tree.

From that literal sense it passes to the energy, spirit, especially of a discourse, the vitality of a speech, the power of language -- something we know Ovid is always concerned with:

sucus 

II. [select] Trop., strength, vigor, energy, spirit: “sucus ac sanguis (civitatis),” Cic. Att. 4, 16, 10: ingenii, Quint. prooem. § 24. —

2. [select] Esp., of the vigor of a discourse, spirit, life: “ornatur oratio ... suco suo,” Cic. de Or. 3, 25, 96.

Below are the seven places where sucus is used. In each, juice drives a metamorphosis, but with differences. Circe's magic potions produce and reverse the transformation of men into boars. Her juices differ from that of the wild olive whose tree imprisons the Apulian shepherd, removing his power of speech. And both of these are different from the natural juices in the trunk of a tree that circulate through the inserted branch that Pomona grafts upon it.

Circe, Glaucus and Scylla
Offended at his rejection of her passion, she at once ground noxious herbs with foul juices, and joined the spells of Hecate to their grinding. (43)

Circe and Odysseus's Men
‘When she saw us, and words of welcome had been received, she smiled at us, and seemed to give a blessing to our desires. Without delay she ordered a drink to be blended, of malted barley, honey, strong wine, and curdled milk, to which she secretly added juices, that its sweetness would hide. We took the cup offered by her sacred hand. As soon as we had drained it, thirstily, with parched lips, the dread goddess touched the top of our hair with her wand, and then (I am ashamed, but I will tell you) I began to bristle with hair, unable to speak now, giving out hoarse grunts instead of words, and to fall forward, completely facing the ground. (275)

Circe reverses charm for Odysseus
‘We were sprinkled with the more virtuous juices of unknown herbs, our heads were stroked with the wand reversed, and the words, she had said, were pronounced, with the words said backwards. The more words she spoke, the more we stood erect, lifted from the ground. Our bristles fell away, our cloven hoofs lost their cleft, our shoulders reappeared, and below them were our upper and lower arms. Weeping we embraced him, as he wept himself, and clung to our leader’s neck, and nothing was said until we had testified to our gratitude. (299)

Circe and Picus's people
She sprinkled them with harmful drugs and poisonous juices, summoning Night and the gods of Night, from Erebus and Chaos, and calling on Hecate with long wailing cries. (402)

The Apulian Shepherd
Nor was his mouth silent till tree-bark imprisoned his throat: he is indeed a tree: you may know its character, by the taste of its fruit that bears the mark of his speech in the wild olives’ bitterness. The sharpness of his words has entered them. (524)

Pomona
She carried a curved pruning knife, not a javelin, with which she cut back the luxuriant growth, and lopped the branches spreading out here and there, now splitting the bark and inserting a graft, providing sap from a different stock for the nursling. (631) 

Vertumnus
But he does not desire now the fruit of your trees, or the sweet juice of your herbs: he desires nothing but you. (690)