四分律行事鈔資持記 3.435

3.435

灰圍應帶微火，有壞種義所故。若食下，次明相種四句。然下，準第二句以示兩通。

The surrounding ash should carry a subtle fire, because it has the sense of destroying the seeds. From "If food..." onward, it next explains the four propositions of recognizable seeds. From "However..." onward, according to the second proposition, it shows that both are permitted.