Baraisa: One may not graft an olive branch even onto the trunk of a female date palm, as it's considered grafting a tree onto a tree.

Question (R. Yudan): Doesn't this disagree with R. Levi, who said - the pasuk states (Tehillim 128:3), "Your wife is like a fruitful vine in the inner chambers of your house; your children are like olive saplings around your table''. Just as olive branches cannot graft with other trees (meaning that if they are grafted, only olives will grow); so too, your children will (not mix with other nations and not have any disqualified offspring. But the Baraisa prohibited grafting with a date palm, which suggests that it can produce a mixed fruit?

Answer: Even though the olive branch cannot successfully graft with the date palm, the date palm can sweeten the olives that grow - like the way that R. Shimon bei Rebbi would water his peach tree with boiled wine in order to sweeten its fruits.

(Mishnah): One may not plant a vegetable on a sycamore stump. One may not graft the Pigam (herb) onto a white Kida tree, as it is considered grafting a vegetable with a tree.

One may not graft a young fig branch onto a Chatzuv, even if his purpose is merely to cool the Chatzuv.

One may not insert an attached vine branch into an Avatiach (watermelon) in order that the water inside it be drawn into the vine branch, as it is considered grafting a tree onto a vegetable.

One may not put a pumpkin seed into Chalamus even in order to protect it (so that it can grow into a pumpkin) as it is considered grafting a vegetable onto a vegetable.

(Gemara) Question (R. Zecharia, son in law of R. Levi): With the reason given, wouldn't it still be prohibited to insert a vine branch into a watermelon, since the vine branch is still connected to the vine, and it is as if he is planting melon seeds under a vine?

Answer (R. Yosi): He distanced the branch 6 Tefachim from the vine and then inserted it 3 Tefachim below the ground into the watermelon.

Support (Baraisa): Pia (herb) roots that are within 4 Tefachim of a vineyard - if they are 3 Tefachim below the ground, they are permitted.