Shatapatha Brahmana 7.5.1.15

7.5.1.15

audumbare bhavataḥ | ūrgvai rasa udumbara ūrjamevāsminnetadrasaṃ dadhātyatho sarva ete vanaspatayo yadudumbara ete upadadhatsarvānvanaspatīnupadadhāti retaḥsicorvelayeme vai retaḥsicāvanayostadvanaspatīndadhāti tasmādanayorvanaspatayaścatuḥsrakti bhavati catasro vai diśaḥ sarvāsu taddikṣu vanaspatīndadhāti tasmātsarvāsu dikṣu vanaspatayo madhye saṃgṛhītam bhavatyulūkhalarūpatāyai

They are made of Udumbara wood;--the Udumbara (ficus glomerata) being strength, life-sap, he thus puts strength, life-sap into him. And, again, the Udumbara being all the trees, by putting on those two, he puts all trees on (the altar). At the distance of the two retahsik (bricks, he places the mortar and pestle),--the 'seed-shedders' being these two (worlds), he thus puts the trees in these two (worlds), and hence there are trees in these two (worlds). It (the mortar) is four-cornered,--there being four quarters, he thus places trees in all the quarters; whence there are trees in all the quarters. It is contracted in the middle, to give it the form of a (real) mortar.