(a) 'Zeisei ...
1. ... Shemen - are olives that one designates for producing oil.
2. ... Kevesh' - are olives that one pickles for eating.
(b) The Mishnah ...
1. ... permits separating Zeisei Shemen on Zeisei Kevesh (see Tosfos Rebbi Akiva Eiger 22 and Bo'az), but ...
2. ... not Zeisei Kevesh on Zeisei Shemen - because they are inferior quality.
(c) By the same token - the Tana forbids separating boiled wine on wine that has not been boiled, buts permits vice-versa.
(a) The principle that governs the above ruling, which permits Ma'asering from good on bad is - that whenever two species are not Kil'ayim together, one is permitted to Ma'aser from the good on to the bad.
(b) One may not however, Ma'aser even from a good species on to a bad one - if the two species form Kil'ayim together.
(c) We learn from the Pasuk in Korach "Kol Chelev Yitzhar ve'Chol Chelev Tirosh" - that each species must be Ma'asered independently (see Tosfos Rebbi Akiva Eiger 24).
(a) With reference to two crops that are not subject to Kil'ayim, if one separated from the bad on to the good - the Terumah is valid.
(b) The only exception to this rule is Zonin (a kind of legumes that grows together with wheat) on wheat - since one tends to feed it to doves.
(c) The Tana Kama considers cucumbers and pickled cucumbers as belonging to one species. Rebbi Yehudah - does not.
(d) The Halachah is - like the Tana Kama.