Canto 1 - Boyhood
Bāla-kāṇḍa
Chapter 14: The Aśvamedha Sacrifice
Text 1.14.39

प्लक्षशाखासु यज्ञानामन्येषां क्रियते हविः।
अश्वमेधस्य यज्ञस्य वैतसो भाग इष्यते॥

plakṣa-śākhāsu yajñānām anyeṣāṁ kriyate haviḥ
aśvamedhasya
yajñasya vaitaso bhāga iṣyate

plakṣa-śākhāsu = using the branches of a plakṣa tree; yajñānām = in sacrifices; anyeṣām = othe; kriyate = is offered; haviḥ = the vapā oblation; aśvamedhasya yajñasya = but for the Aśvamedha sacrifice; vaitasaḥ = of a vetasa reed; bhāgaḥ = using a part; iṣyate = it is offered.

The vapā oblation in other sacrifices is offered using the branches of a plakṣa tree. But for the Aśvamedha sacrifice, it is offered using a part of a vetasa reed [26].

A part of the vetasa reed is used to place the vapā in the case of the Aśvamedha sacrifice [27].

[26] plakṣa-śākhāyām anyeṣāṁ paśūnām avadyanti vetasa-śākhāyām aśvasya. (Śruti)

[27] vaitasaḥ kaṭo bhavati apsu yonir āśvaḥ apsu jo vetasaḥ sva evainaṁ yonau pratiṣṭhāpayati. (Śruti) vaitasa-kaṭe ’śvaṁ prāñcam āsādayati. (Āpastamba Śrauta-sūtra)