成唯識論演祕 6.459

6.459

顯具二理，即本末二名言之種，而由能熏七識熏得此所熏種，而後能生本末現識，故本末二得有能生、所生二義。

This shows the possession of the two principles: namely, the two conventional bījas of root and branch, through which the perfuming seven consciousnesses perfume these perfumed bījas, which subsequently can generate the present root and branch consciousnesses; hence, root and branch come to have the two meanings of capable of generating and that which is generated.