Charles Ellicott Commentary Leviticus 11:37

"And if [aught] of their carcass fall upon any sowing seed which is to be sown, it is clean." — Leviticus 11:37 (ASV)

And if any part of their carcass. —The principle that underlies the immunity from pollution of living water is also at the basis of the exception for living plants. Hence, if the carcass or a portion of a dead reptile is found among grain destined for sowing, the quantity of wheat in which it is discovered does not become defiled, since the growing plant constantly derives new elements from below and fresh moisture from above, thus undergoing as many changes in its development as spring water.

The law, therefore, that was in effect during the Second Temple was as follows: “Whatever is fixed in the ground does not contract defilement. Plants are not defiled until they are gathered.” Hence, the ancient Chaldee version of Jonathan renders this verse: “If any part of their carcass falls upon any seed that is sown in the manner in which it is commonly sown—that is, in its dry state—it is clean.”