In a mantra the final of oṣadhi is lengthened before the case-endings but not in the Nominative 1st-Case.,
Thus ओषधीभिरपीपतत्, नमः पृथिव्यै नमः ओषधीभ्यः ॥ Why do we say 'before case-endings'? Observe ओषधिपते ॥ Why do we say 'but not in the Nominative'? Observe स्थिरेयमस्त्वौषधिः ॥,