We are up to Maseches Orlah, chapter 1, mishnah 9. In this mishnah Rabbi Yosi teaches us three laws concerning planting and grafting in the context of orlah, and through them his consistent position regarding fruit that has not yet ripened comes to light.
Planting a shoot and planting a nut:
"Notin yichur shel orlah" - a yichur is a branch taken from a tree that is within its first three years, and one is permitted to plant it. The reason: the branch is nothing more than wood, and the wood of an orlah tree is permitted for benefit. Therefore, even though a person derives benefit from it, there is no prohibition here, since this is not benefit from the fruit of the tree but from the tree itself.
"V'ein notin egoz shel orlah, mipnei shehu peri" - the nut itself is considered the fruit of that tree, and it is therefore forbidden as orlah, so planting it constitutes forbidden benefit.
"V'ein markivin b'chafniyos shel orlah":
It is worth prefacing that grafting between two different species is forbidden by law, whereas grafting within the same species is permitted. Even so, the mishnah rules that one may not graft with chafniyos. Chafniyos are branches of a date palm bearing dates that have not yet fully ripened, and their status is like that of the semadar, the stage we discussed in the previous mishnah with regard to an unripe grape. These, then, are young dates that have not ripened.
And the reason for the prohibition: we are concerned that a person may come to eat from these chafniyos, that is, from the young, unripe dates, and these are considered forbidden as orlah.
Rabbi Yosi's consistent position:
This ruling is a continuation of Rabbi Yosi's position that was mentioned in the mishnah we learned earlier. There the Tanna Kamma held that the semadar of grapes is permitted, and Rabbi Yosi disagreed and said that it is considered forbidden as orlah. Here too, when he comes to discuss dates, Rabbi Yosi again rules that they are forbidden as orlah, for in his view the status of fruit at the semadar stage, whether in a grape or in a date, is forbidden and considered orlah.
In summary: in this mishnah we learned three laws: planting a shoot of orlah is permitted, because the branch is wood and not fruit; planting a nut is forbidden, because the nut is fruit; and one may not graft with chafniyos, dates at the semadar stage, out of concern that one may come to eat them. In all of these, Rabbi Yosi's position comes to light: that fruit at the semadar stage is forbidden as orlah.