The Vatican Fragments are a collection of legal texts, found in the Vatican library by cardinal Angelo Mai in 1821, and published by him in 1823.

Fragment 233
Ulpianus de officio praetoris tutelaris. Sed qui in collegio pistorum sunt a tutelis excusantur, si modo per semet ipsos pistrinum exerceant; sed non alios puto excusandos, quam intra numerum constituti centenarium pistrinum secundum litteras divi Traiani ad Sulpicium Similem exerceant; quae omnia litteris praefecti annonae significanda sunt. Ulpian, in his commentary on the official function of the praetor tutelaris. Yet those in the collegium pistorum are exempted from guardianship if they themselves operate a pistrinum, but I believe that no others can be released apart from those among their number who operate a pistrinum of 100,000 sesterces in accordance with the letter of the late Trajan to Sulpicius Similis. And all these matters are given in a letter to the Prefect of the Annona.

Translation: A.J.B. Sirks, Food for Rome, p. 315.

Fragment 234
Ulpianus libro supra scripto. Sed Ostienses pistores non excusantur, ut Philumeniano imperator noster cum patre rescripsit. Ulpian in the above mentioned book [= Duties of the Praetor Tutelaris]. Yet the bakers from Ostia are not exempted, as our Emperor together with his father [Septimius Severus and Caracalla] had decreed by rescript to Philumenianus.

Translation: A.J.B. Sirks.