Śatapatha Brāhmaṇa ("of a hundred paths") 3.7.1.12

3.7.1.12

atha caṣālamubhayataḥ pratyajya pratimuñcati | supippalābhyastvauṣadhībhya iti pippalaṃ haivāsyaitadyanmadhye saṃgṛhītamiva bhavati tiryagvā idaṃ vṛkṣe pippalamāhataṃ sa yadevedaṃ sambandhanaṃ cāntaropenitamiva tadevaitatkaroti tasmānmadhye saṃgṛhītamiva bhavati

Having then anointed the top-ring on both sides, he puts it on (the stake) with, 'To the full-berried plants--thee!' for that (top-ring) is as its berry. And as to its being, as it were, contracted in the middle, the berry here on trees is fastened (to the stalk) sideways; what connecting part there is between (the fruit and stalk) pressed in, as it were, that he thereby makes it. This is why it is, as it were, contracted in the middle.