Ante-Nicene Fathers, Vol VI:
VI.--Of the One Substance.

VI.-Of the One Substance.¹

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The plant that springs from the root is something distinct from that whence it grows up; and yet it is of one nature with it. And the river which flows from the fountain is something distinct from the fountain. For we cannot call either the river a fountain, or the fountain a river. Nevertheless we allow that they are both one according to nature, and also one in substance; and we admit that the fountain may be conceived of as father, and that the river is what is begotten of the fountain.²