Before us is Mishnah 1 in chapter 7 of Maseches Nedarim, which deals with the question of what is included in the category of "vegetable" with regard to vows, and with the dispute among the Tannaim concerning gourds.
The Wording of the Mishnah and the Dispute of the Tannaim:
"HaNoder Min HaYarak - Mutar B'Dilu'in" - according to the first Tanna, one who takes a vow against vegetables is permitted to eat gourds, since gourds are not included in the category of "vegetable"; the meaning of "vegetable" is leafy greens. "V'Rabbi Akiva Oser" - according to Rabbi Akiva gourds are forbidden, meaning that gourds are included in the category of vegetables. The Mishnah thus presents a dispute between the first Tanna and Rabbi Akiva, and explains the reasoning of each side.
The Proof of the Sages:
The Sages, who hold like the first Tanna that gourds are permitted, said to Rabbi Akiva: "V'Halo Omer Adam LiShlucho: Kach Li Yarak, V'Hu Omer: Lo Matzasi Ela Dilu'in" - a person sends his agent to the market to buy him vegetables, and the agent comes back and reports that he found nothing but gourds. From the wording of that report it is evident that gourds are not included in the category of vegetables, for the agent testifies about himself that he did not find any vegetables.
Rabbi Akiva's Answer:
"Amar Lahem: Ken HaDavar" - Rabbi Akiva concedes that this is indeed so, that the agent does not buy the gourds on his own initiative but rather comes back and reports about them. But there is a fine point to consider: "O Shema Omer Hu Lo: Lo Matzasi Ela Kitnis?" - would it enter anyone's mind that the agent would come back and report that he found nothing but legumes? Legumes are obviously not included in the category of vegetables, and a person does not bother to report about something that has no connection at all to the request - just as he would not report back that there was no cattle there, and would not report about something that bears no relation to vegetables.
"Ela SheHaDilu'in Bichlal Yarak" - the reason he reports specifically about gourds is because gourds are included in the category of vegetables, only that they are not the type of vegetable that the sender had in mind. Therefore the agent comes back and informs him: all I found was a vegetable of the gourd variety, and let the sender tell me whether this is what he wants or not. "V'Ein HaKitnis Bichlal Yarak" - legumes, however, are not included in the category of vegetables at all, and therefore there is no reason to report about them.
The Egyptian Bean - Moist and Dry:
The Mishnah concludes with a further distinction in the definitions of vegetables:
"V'Assur B'Pol HaMitzri Lach" - one who vows against vegetables is forbidden to eat the Egyptian bean as long as it is moist, since in that state it is counted among the family of vegetables and not among the family of legumes.
"U'Mutar B'Yavesh" - once it has dried out, it is no longer part of the vegetable family but of the legume family, and therefore one who vows against vegetables is permitted to eat it.
In summary: in this Mishnah we learned the dispute between the first Tanna and Rabbi Akiva regarding one who vows against vegetables - whether gourds are included in that category. The Sages proved from the agent's wording, "I found nothing but gourds," that gourds are not included in the category of vegetables, and Rabbi Akiva responded that on the contrary: the very fact that he reports about them proves that gourds are included in the category of vegetables, for about legumes he would not have reported at all. We also learned the distinction regarding the Egyptian bean - forbidden when moist, since it is then in the category of vegetables, and permitted when dry, since it is then in the category of legumes.