Any person entitled to a lien under this act¹ shall, within thirty (30) days after the threshing or combining is completed, file in the office of the county clerk of the county in which the grain or seed was grown, or threshing or combining done, a statement in writing, verified by oath, showing the amount, quantity and kind of grain or seed threshed or combined, the price agreed upon for the threshing or combining the same, the name of the person for whom the threshing or combining was done, and a description of the land on which the grain or seed was grown or threshing or combining done; unless the person entitled to the lien shall file such statement within the time aforesaid, he shall be deemed to have waived his rights thereto; provided, that the lien provided for in this act shall not attach to any seed or grain after it has been purchased by a grain dealer and has passed into his possession unless the lien shall have been filed with the county clerk of the county before the seed or grain was purchased by such dealer, or he shall have received written notice from the party entitled to the lien, of his intention to file the same.