Śatapatha Brāhmaṇa ("of a hundred paths") 1.3.3.10

1.3.3.10

tadvai bahulaṃ stṛṇīyādityāhuḥ yatra vā asyai bahulatamā oṣadhayastadasyā upajīvanīyatamaṃ tasmādbahulaṃ stṛṇīyāditi tadvai tadāhartaryevādhi trivṛtstṛṇāti trivṛddhi yajño 'tho api pravarhaṃ stṛṇīyātstṛṇanti barhirānuṣagiti tṛṣiṇābhyanūktamadharamūlaṃ stṛṇātyadharamūlā iva hīmā asyām pṛthivyāmoṣadhayaḥ pratiṣṭhitāstasmādadharamūlaṃ stṛṇāti

Here now they say, 'Let him strew abundantly; for where the plants are most abundant on her, there the means of subsistence are most amply afforded by her: let him therefore strew abundantly!' It is in favour of him (the sacrificer) who procures (the sacrificial grass), then, (that this is done.) He strews it threefold, for threefold is the sacrifice. Or he may also spread it whilst lifting up (the tops); for it has been said by the seer (Vâg. S. VII, 32), 'They spread the barhis continuously.' He spreads it with the roots below (the tops); for it is with their roots below that those plants are firmly established in this earth: for this reason he spreads it with the roots below.