A.T. Robertson Commentary Mark 4:26

"And he said, So is the kingdom of God, as if a man should cast seed upon the earth;" — Mark 4:26 (ASV)

As if a man should cast (ως ανθρωπος βαλη). Note ως with the aorist subjunctive without αν. It is a supposable case and so the subjunctive and the aorist tense because a single instance. Blass considers this idiom "quite impossible," but it is the true text here and makes good sense (Robertson, Grammar, p. 968). The more common idiom would have been ως εαν (or αν).