When it is sown (otan sparh). Second aorist passive subjunctive of speirw. Alone in Mark and repeated in verse Matthew 32 . Less than all the seeds (mikroteron pantwn twn spermatwn). Comparative adjective with the ablative case after it. Hyperbole, of course, but clearly meaning that from a very small seed a large plant grows, the gradual pervasive expansive power of the kingdom of God.