R. Zeira and R. Ila/ R.Elazar quoting R. Hoshiya disagreed over why the Rosh Hashanah for trees is the 15th of Shevat - One said that most of the rains of that entire year have already fallen (and the sap has risen in the trees thereby causing the fruits to begin budding) even though most of the season has not yet passed.

The other one said that until this point, the fruits have grown from the rains that fell in the previous year; but from the 15th of Shevat, the fruits grow from this year's rains.

Question: We do not know which Chacham said each of these explanations.

Answer: From the statement of R. Yasa/ R. Ila/ R. Elazar quoting R. Hoshiya that the reason is that most of the rains of that entire year have already fallen etc....this shows that R. Zeira gave the other reason, that until then the fruits have grown from the previous year's rain etc.

There was a story of R. Akiva who picked an Esrog and treated it with the stringencies of both Beis Shamai and Beis Hillel (who disagree over which day is the Rosh Hashanah of the trees. During the 2nd year of the Shemita cycle one separates Maaser Sheni. In the 3rd year one separates Maaser Ani (for the poor). Beis Shamai hold that the new year falls on the 1st of Shevat, meaning that after that one must separate Maaser Ani after the 1st. Beis Hillel hold that it is on the 15th of Shevat, but before that one still separates Maaser Sheni. R. Akiva would separate both types of Maaser during those two weeks.)

Question: Why was this only done to an Esrog - for any tree this should also apply?

Answer (Beraisa): (It is not because of the dispute of Beis Shamai and Beis Hillel, rather) he was stringent for the opinions of both Rabban Gamliel (that the Maaser of an Esrog follows the time it was picked) and R. Eliezer (that its Maaser follows the time it budded).

Question: Did Rabban Gamliel and R. Eliezer disagree with Beis Hillel? (Surely they agree with him - if so, when he picks it on the 1st of Shevat, both the budding and the picking occurred in the same year i.e. the 2nd year)!

Answer (R. Yosa bei R. Bun): When it budded before the 15th of Shevat of the 2nd year coming into the 3rd year (and he picked it after the 15th)...

According to R''G, one must separate Maaser Ani, as an Esrog follows its picking.

According to R. Eliezer, one must separate Maaser Sheni.

What did R. Akiva do? He declared part of it to be Maaser Sheni and then redeemed it onto money and gave that money to a poor man.