The Gemara in [Gittin 22a](https://www.sefaria.org/Gittin.22a.12?lang=bi&with=all&lang2=en) brings a machlokes in regard to fruits getting nutrients from a tree that is half in ארץ ישראל and half in חוץ לארץ.

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> ומאי טעמא דרשב"ג דמפסיק צונמא  
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> מאי טעמא דרבי דהדרי ערבי
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> רשב"ג says since there is a rock between the roots, the nutrients are divided accordingly.  
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> רבי says even though there is a separation, it isn't possible to tell which nutrients go where.
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How can they argues on how a tree works, isn't it just facts?