I was wondering whether there is any difference between the following partitive expressions in Latin: ūnus tribūnōrum and ūnus ex tribūnīs 'one of the tribunes' (cf. the so-called 'partitive genitive' and prep. ex + ablative, respectively).
Another related question is whether there is any difference between the following use of ex and de: e.g., cf. unus ex captivis (Caes. Gall., 6, 35, 8) and nulla de virtutibus tuis plurimis (Cic. Pro Lig. 37).
Are there any subtle differences involved? If so, could you please recommend any bibliographical source where these are mentioned/described?