Śatapatha Brāhmaṇa ("of a hundred paths") 3.8.3.12

3.8.3.12

tasyāvāṅ medhaḥ papāta | sa eṣa vanaspatirajāyata taṃ devāḥ prāpaśyaṃstasmātprakhyaḥ prakhyo ha vai nāmaitadyatplakṣa iti tenaivainametanmedhena samardhayati kṛtsnaṃ karoti tasmātplakṣaśākhā uttarabarhirbhavanti

Its sacrificial essence flowed down and there a tree sprang up. The gods beheld it; wherefore it (was called) 'prakhya' (visible), for 'plaksha,' doubtless, is the same as 'prakhya.' With that same sacrificial essence he now completes it (the victim), and makes it whole: hence there are Plaksha branches as an upper covering.