Ulmus vocatur, ut dicit Ysidorus, quod vim habet multam viroris. Natura enim ipsius talis est, ut etiam arefacta, si abluatur, reviviscat. Deinde excisa atque in humo fixa radicibus sese ipsa demergit.
Concerning the elm tree. It is called the elm tree, as Isidore says, because it has great strength of verdure. Indeed, its nature is so great that even having been dried up, if it is refreshed, it comes to life again. After having been cut apart and having been fixed in the ground by the roots, it settles itself.
abluo, abluere, ablui, ablutus 3 to quench; refresh
arefacio, arefacere, arefei, arefactus 3 io to dry up; to wither up
demergo, demergere, demersi, demersus 3 to submerge, to immerse, to set
excido, excidere, excidi, excisus 3 to cut off; to cut apart
humus, humi f. ground; soil
radix, radicis f. root
ulmus, ulmi f. elm tree
viror, viroris m. verdure; fresh green quality
Ysidorus: Isidore of Seville, a 6th century scholar and Archbishop who wrote an etymological encyclopedia that included information on the natural world.
quod: causal quod, “beacuse…”
ut etiam…reviviscat: result clause with talis. “Indeed, the nature of it [the elm tree] is so great that even having been dried up, if watered, it comes to life again.” This is why reviviscat is subjunctive.
demergit: this is referring to the elm tree’s supposed ability to re-grow from cut branches. Though demergit means to immerse or to set, the implication is that its roots are settling and stabilizing themselves.