If I use too much of the lingo of my studies, please ask or correct me or something.
aut tonsum tristi contingunt corpus amurca
et spumas miscent argenti vivaque sulpura
Idaeasque pices et pinguis unguine ceras
All the capital manuscripts of Vergil read et sulpura viva; I don't have access to Geymonat's edition, so I cannot say what the Carolingian mss. say, except that Ribbeck in his edition quotes Beda with et sulpura viva.
One will of course notice this one point: the printed text here isn't exactly easy to scan, in fact we have to accept a hypermetrum that in my eyes isn't attractive at all, since the anceps now scans short.
Consider, however, the indirect evidence (in rough chronological order):
Victorinus writes in his de metris et de hexametro, GLK VI.212:
...ultimo pede, quem necesse est disyllabum esse, ne contra rationem supra dictam syllabarum amplior numerus adcrescat. Quid ergo? numquamne dactylus in fine ponitur? Ponitur quidem; verum non in eo versu qui ceteros dactylos habet in se, veluti est ille in Georgicis:
et spumas miscent argenti vivaque sulpura
quem quidam invertentes sic legunt et sulpura viva.
Re-reading this, it sounds like total gibberish: of course we never see a dactyl in the sixth foot, a hexametre is always catalectic. His next example, Aen.6.33, however, is also an example of a hypermetrum, which justifies his reading if not his argument.
Servius (with DServius in italics) in his commentary writes ad locum:
vivaqve svlpvra dactylicus versus, quod in fine dactylum habeat.
Exactly the same as Victorinus. Servius uses the same terminus for the hypermetric verse in one other place, ad Georg.2.69:
fetv nvcis arbvtvs horrida versus dactylicus: nam male quidam 'horrens' legunt.
It's beginning to look like a real terminus technicus, but it's just such a misleading name!
No matter, let's look at the next piece of evidence, Macrobius Saturnalia 5.14.4:
ὑπερκαταληκτικοὶ <versus> syllabâ longiores sunt:
(Aen.6.33) ...quin protinus omnia
(Georg.1.295) ...Vulcano decoquit umorem
(Georg.3.449) spumas miscent argenti vivaque sulphura
(Georg.2.69) ...arbutus horrida
Ok, let's just check out Servius at the one place we haven't seen so far, Georg.1.295:
Vulcano decoquit umorem hypermetrus versus: unde et sequens a vocali inchoat. <...> et aliter: hic versus longior est una syllaba, sed sine vitio, quoniam sequens a vocali incipit.
Same definition, even word for word in DServ., but different nomenclature. Difference here is of course that umorem has a long o.
Last place to cite our verse, the Scholia Bernensia, a collection of scholia from the tenth cent., I think.:
et spumas miscent argenti vivaque sulphura dactylicus versus
Back to the terminus of Victorinus.
Mynors in his edition cites one, and just one reading from a Carolingian manuscript, his r, which has viva et sulpura, which is even harder to scan, being spondaic and all.
Now, this is about as comprehensive an account as possible of the direct evidence and the grammarians' citations. Only one piece of 'intertextual evidence' (or whatever you wish to name it) have I been able to find, Quintus Serenus, liber medicinalis 35:
aut tu fenuculum nitrumque et sulphura viva
Sulphura is most commonly found as the fifth foot of a hexametre: Silius, 13.568; Ovid, Met, 1.271, 3.370, 14.783, 15.342; Juv. 5.46; Dracontius, Medea, 484; Claudius Marius Victorius, Alethia, 2.127, 3.733, 763; App.Verg., Ciris, 369; Calp.Sic., 5.78.
This list only takes notice of writings from the fifth century or earlier.
So now it all boils down to this one question, which Victorinus and all this evidence inevitably asks us:
If you were to edit the text of Vergil's Georgics, would you join Victorinus, Servius, Servius Danielinus (who might have been Donatus), Macrobius and the Berne Scholiast and write vivaque sulpura, or would you be one of the quidam who preferred the 'metric' reading with no indirect evidence but the evidence of three manuscripts that have survived the centuries since before the fall of Rome and countless examples of sulpura in the fifth foot, including one writer (from the third century) who chose to copy Vergil's words in the easier, metrical version?