Gemara

(Beraisa): Small bitter almonds are Tevel. (One must tithe them.) Large ones are exempt. Large sweet almonds are Tevel. Small ones are exempt.

Version #1 (R. Yishmael b'Rebbi Yosi): Both [small or large almonds that are bitter] are exempt.

Version #2 (R. Yishmael b'Rebbi Yosi): Both are Tevel.

Question: [In version #2,] why are they Tevel? They are not proper to eat!

Answer (R. Yochanan): They can be sweetened through cooking.

Berachos 36b (Mishnah): Orlah applies to pomegranate peels, the Netz (a flower around the stem), nut shells and pits.

Rishonim

Rosh (Berachos 6:4) and R. Yonah (Berachos 25b DH umid'Legabei): Orlah applies to pomegranate peels, the Netz, nut shells and pits. This shows that pits are Pri. One blesses Borei Pri ha'Etz on all pits, as long as they are not bitter, so one enjoys them.

R. Yonah (ibid.): If they are bitter, one does not bless on them at all.

Rosh (Hilchos Orlah 7): Orlah applies to all pits. They are exempt from [Kedushas] Revai (fourth-year produce of vines or trees), for a Beraisa obligates only Pri.

Rashba (36b DH Klipei): Tosfos learns from here that one blesses Borei Pri ha'Etz on pits of cherries, peaches, apples and all Peros. This is wrong. They are Chayav in Orlah, but not because they are Pri. Rather, a Drashah includes them, for they are Tefel (secondary to) the Pri! This is why they were taught along with shells of nuts. All are included from "Es". The pits of cherries and peaches are bitter. We do not bless on them at all, for people do not plant [these trees] with intent to eat the pits at all! If one sweetens them through fire, one blesses sheha'Kol.

Poskim

Shulchan Aruch (OC 202:3): If pits are sweet, one blesses on them Borei Pri ha'Etz.

Beis Yosef (DH v'Al): Tosfos, the Mordechai, Rosh and R. Yonah say that one blesses Borei Pri ha'Etz. The Tur brings that the Rashba disagrees.

Gan ha'Melech (30): Orlah 1:8 says that Orlah applies to pomegranate rinds, the Netz, nut shells and pits. They are forbidden in an Asherah (a tree forbidden due to idolatry) and [peels and pits of grapes are forbidden] to a Nazir. They are permitted in Revai. The Bartenura says 'Orlah applies, because "Es Piryo" includes what is Tefel to the Pri. They are permitted in Revai, for Revai does not forbid Hana'ah. The owner may eat them in Yerushalayim like Ma'aser Sheni, and Ma'aser Sheni applies only to what is proper to eat.' This implies that these are not Pri. Therefore, they are permitted regarding Revai. The Drashah forbids regarding Orlah, even though they are not edible, e.g. grape pits, pomegranate rinds and nut shells. Orlah depends on Hana'ah. One may not even dye a garment with peels of Orlah. Why does Tosfos learn from Orlah to Berachah? If so, we should bless Borei Pri ha'Etz on soft nut shells, for they are equated to the seeds! The primary Berachah of the Pri is only for what the tree is planted for. Presumably, it is not planted for the pits. Orlah is very different. Orlah applies to dates and Novlos (dates that dried up due to the sun, or were detached by the wind) of Tzlaf (caper), even though we bless Borei Pri ha'Adamah and sheha'Kol on them, respectively. Therefore, I say to bless only Borei Pri ha'Adamah on the seeds. Do not say that it is sheha'Kol, like Kora (shoots of a date tree). Kora is different, for there is a loss to the tree [if one removes it]. For seeds, it suffices to lower the Berachah from Borei Pri ha'Etz to Borei Pri ha'Adamah. Even though the Gemara learns Orlah from Berachos, this is only to show that what is important regarding Berachah, for it is considered Pri, is important for Orlah. We cannot learn from Orlah to Berachah.

Mishnah Berurah (23) and Sha'ar ha'Tziyun (22,23): They need not be sweet. It suffices that one enjoys eating them. The Gra (Orlah 3:1) and many Acharonim (e.g. Even ha'Ozer) say to bless Borei Pri ha'Adamah. If one blessed Borei Pri ha'Etz, he was Yotzei. If one ate the Pri and then the pit, all (even the Rashba) agree that he was Yotzei through the Berachah on the Pri.

Kaf ha'Chayim (37): He was Yotzei because Safek Berachos Lehakel. It is best to bless sheha'Kol on something else to exempt the pits.

Shulchan Aruch (ibid.): If they are bitter, one does not bless on them at all. If one sweetened them through fire, one blesses sheha'Kol.

Magen Avraham (7): This is difficult. The Rashba says that if one sweetened them through fire, one blesses sheha'Kol. This is based on his opinion, that seeds are not Pri. We hold like the Rosh. If so, after one sweetened them through fire, one blesses Borei Pri ha'Etz, like it says in Sa'if 5 about almonds! We must say that when they are bitter they are not Pri, unlike almonds. The Levush connotes like this.

Even ha'Ozer: The Magen Avraham should challenge the Rashba from roses. They are not the primary Pri, and they are not eaten raw, but after cooking them in honey, one blesses Borei Pri ha'Adamah. The same should apply to pits! Rather, the Rashba wrote that it is because people do not plant them for the pits. This is even if they are proper to eat. Also we [who hold like the Rosh] say sheha'Kol on pits for this reason. The Beis Yosef brought Teshuvas ha'Rashba (1:400) that on moist peppers we bless Borei Pri ha'Adamah, and not Borei Pri ha'Etz, for they are planted to eat them dry. If they were planted without any intent for them at all, their Berachah would be sheha'Kol. Fruits with edible pits are planed with intent to eat them with the pits. The Tur connotes that one blesses Borei Pri ha'Adamah on them.

Yad Efrayim: The Magen Avraham intended like Even ha'Ozer says. He says that when they are bitter they are not Pri, i.e. people do not plant with intent for them. There is a side to say that even though they are not planted with intent to sweeten them, this does not matter, since there is intent for the fruit. The Rashba (1:428) says so about unripe grapes, since one eats the fruit for whose sake they are planted.

Even ha'Ozer: Uktzim 2:2 says that pits do not join for Tum'as Ochlim. Perush ha'Mishnayos says that this is even for edible pits, e.g. of pears. The Yerushalmi says that Terumos 11:5, which permits discarded pits of Terumah, refers to edible pits.

Gra (DH v'Im): The first law is like Tosfos, and the latter is like the Rashba, like the Magen Avraham asked! The Rashba's opinion is primary. The Stam Mishnayos in Terumos (11:5) and [the same applies to] Bikurim (Chulin 120b) and Uktzim (2:2) teach that pits are not Pri at all. Another proof is that they are permitted regarding Revai. This shows that they are forbidden regarding Orlah only due to an inclusion of the verse.

Taz (204:15): Tosfos and the Rosh say that Kafrisin are Pri. Orlah applies to them without an inclusion. They are better than nut shells, which needed an inclusion to obligate them in Orlah, since they are a Shomer. Abaye proved that the Netz is not a food, and then challenged Rava from the Mishnah, which says that Orlah applies to the Netz, even though it is not a Shomer once the Pri is detached. Had he not shown that it is not a food, he would have no question, for a food is like the Pri itself. The same applies to Kafrisin. If so, one should bless Borei Pri ha'Etz on them! Tosfos did not say to bless Borei Pri ha'Etz on nut shells, for they are not a food. They are included only for Orlah, but not for Berachah. Therefore, one blesses Borei Pri ha'Adamah on them.

Panim Me'iros (1:65): Pits are not a Shomer. We must say that they are included for Orlah because they are Pri. If so, one blesses Borei Pri ha'Etz on them. The Rosh explicitly says so, as long as they are not bitter. How did Tosfos and the Rosh learn from Orlah to bless Borei Pri ha'Etz on all pits? If so, Revai should apply to them! Also, Orlah applies even to pits [so one should bless Borei Pri ha'Etz on them]! We must say that even though they are not a Shomer, the verse did not mention a Shomer. It taught about what is Tefel to the Pri. We include pits that are also Tefel to the Pri. The Rosh himself [in Hilchos Orlah] says that Orlah applies to all pits, but Revai does not, for one must redeem only Pri. (Also Ma'adanei Yom Tov Berachos 6:50 asked this.) Perush ha'Mishnayos says that Orlah applies to pomegranate rinds and the Netz, not because they are Pri, rather, because they can be used to dye, and one may not dye with Orlah. All are permitted in Revai, for it applies only to edible Pri. This connotes that all pits are not considered Pri. How can one bless Borei Pri ha'Etz? One should bless only sheha'Kol, or Borei Pri ha'Adamah according to the Rashba. Terumos 11:5 says that if one discarded Terumah pits, they are permitted. This is even if though they are edible. If they are Pri, a Zar may not eat them! Rather, even edible pits are not Pri.

Pri Chodosh (Likutim 202:3): Perhaps Tosfos distinguishes pits from bitter almonds. People do not plant for the sake of pits. (Therefore, even after sweetening pits through fire, the Berachah is only sheha'Kol.) However, this is unreasonable. If so, even when they are naturally sweet the Berachah should be sheha'Kol, like Kora. The Rashba is primary. The Rosh retracted to say like the Rashba in Hilchos Orlah. This is primary, unlike the Shulchan Aruch.

Birkei Yosef (3): Many Acharonim hold like the Rashba, who rejected Tosfos. To avoid the argument, one should bless sheha'Kol. The Pri Chodosh and Gan ha'Melech say to bless Borei Pri ha'Adamah, but since we are concerned for the opposing opinion, it is proper to bless sheha'Kol.

Mishnah Berurah (24): Bitter means that they are not proper to eat even in pressed circumstances.

Mishnah Berurah (25): Since many say to bless only Borei Pri ha'Adamah on sweet pits, one should bless only sheha'Kol on bitter pits that were sweetened, like the Shulchan Aruch.