From a garden conversation in New Vrindaban June 22, 1976; see the whole conversation here.

I wasn’t at this one, as there were so many devotees we were taking turns attending them. I wish someone had mentioned the bitter melon comment to me back then as it wsa too many years later before I got into them.

Prabhupāda: Difference is it is Kṛṣṇa’s desire. He wants that “Don’t remain like cats and dogs. Be intelligent and come back to Me.” Kṛṣṇa says sarva-dharmān parityajya mām ekam śaraṇaṁ vraja BG 18.66 . So it is the duty of a devotee of Kṛṣṇa to spread this knowledge so that they may take to Kṛṣṇa. The cats and dogs, they cannot understand, but those who are two-legged cats and dogs, (laughs) they can understand. That is the advantage, because they have got two legs. So long they had four legs (laughing) they could not understand. So here is a chance, two-legged, so give them some opportunity. That’s all. (long pause) You grow bitter melon also here?

Kīrtanānanda: We tried to this spring to grow it, but we can’t get the seed to sprout.

Prabhupāda: You can get it from Māyāpura?

Kīrtanānanda: We got seed, but it won’t sprout.

Prabhupāda: Oh, due to the climate.

Kīrtanānanda: We don’t know. It is a very hard seed.

Devotee (4): Śrīla Prabhupāda, perhaps the material scientists could help us make the seed sprout.

Prabhupāda: Hmm?

Devotee (4): I was thinking earlier how a farmer can put the seed in the ground, but he cannot actually make the seed grow if it is not the will of Kṛṣṇa.

Prabhupāda: Yes. The situation is not favorable. That is the proof that everything is a living entity. If you put the seed… The seed is not the tree, but when you put the seed on the ground, if the situation is favorable, the particular living entity who has to take the form of that tree, he comes, and then it grows. That is the proof. Just like sex. It is not the secretion of the man and the woman. It creates a situation so that the soul may come and live there, and then there is pregnancy. It is not the matter. This is the proof.