Chandogya Upanishad 5.49

अभ्रं भूत्वा मेघो भवति मेघो भूत्वा प्रवर्षति त इह व्रीहियवा ओषधिवनस्पतयस्तिलमाषा इति जायन्तेऽतो वै खलु दुर्निष्प्रपतरं यो यो ह्यन्नमत्ति यो रेतः सिञ्चति तद्भूय एव भवति ॥ ६ ॥

5.10.6 — abhram bhutva megho bhavati megho bhutva pravarshati ta iha vrihiyava oshadhivanaspatayastilamasha iti jayante'to vai khalu durnishprapataram yo yo hyannamatti yo retah sinchati tadbhuya eva bhavati || 6 ||

After having become mist, he becomes cloud. After having become cloud, he rains down. They are born here as rice and barley, as herbs and trees, as sesame plants and beans. Thence, verily, indeed, it is difficult to emerge; for only if some one or other eats him as food and emits him as semen, does he develop further.

'अभ्र होकर मेघ बनते हैं; मेघ होकर बरसते हैं। तब वे यहाँ व्रीहि, यव, औषधि, वनस्पति, तिल, माष आदि के रूप में उत्पन्न होते हैं। वहाँ से निकलना अत्यन्त कठिन होता है — क्योंकि जो अन्न खाता है और जो रेत सींचता है, उसी के द्वारा वह पुनः बनता है।'