2 “Let the earth bring forth grass yielding seed after his kind.” So that although some kind of grass is of service to animals, even their gain is our gain too, and seeds are especially designed for our use. Such is the true meaning of the words that I have quoted. “Let the earth bring forth grass, the herb yielding seed after his kind.” In this manner we can re-establish the order of the words, of which the construction seems faulty in the actual version, and the economy of nature will be rigorously observed. In fact, first comes germination, then verdure, then the growth of the plant, which after having attained its full growth arrives at perfection in seed.
How then, they say, can Scripture describe all the plants of the earth as seed-bearing, when the reed, couch-grass, mint, crocus, garlic, and the flowering rush and countless other species, produce no seed? To this we reply that many vegetables have their seminal virtue in the lower part and in the roots. The need, for example, after its annual growth sends forth a protuberance from its roots, which takes the place of seed for future trees. Numbers of other vegetables are the same and all over the earth reproduce by the roots. Nothing then is truer than that each plant produces its seed or contains some seminal virtue; this is what is meant by “after its kind.” So that the shoot of a reed does not produce an olive tree, but from a reed grows another reed, and from one sort of seed a plant of the same sort always germinates. Thus, all which sprang from the earth, in its first bringing forth, is kept the same to our time, thanks to the constant reproduction of kind.
“Let the earth bring forth.” See how, at this short word, at this brief command, the cold and sterile earth travailed and hastened to bring forth its fruit, as it cast away its sad and dismal covering to clothe itself in a more brilliant robe, proud of its proper adornment and displaying the infinite variety of plants.
I want creation to penetrate you with so much admiration that everywhere, wherever you may be, the least plant may bring to you the clear remembrance of the Creator. If you see the grass of the fields, think of human nature, and remember the comparison of the wise Isaiah. “All flesh is grass, and all the goodliness thereof is as the flower of the field.” Truly the rapid flow of life, the short gratification and pleasure that an instant of happiness gives a man, all wonderfully suit the comparison of the prophet. Today he is vigorous in body, fattened by luxury, and in the prime of life, with complexion fair like the flowers, strong and powerful and of irresistible energy; tomorrow and he will be an object of pity, withered by age or exhausted by sickness. Another shines in all the splendour of a brilliant fortune, and around him are a multitude of flatterers, an escort of false friends on the track of his good graces; a crowd of kinsfolk, but of no true kin; a swarm of servants who crowd after him to provide for his food and for all his needs; and in his comings and goings this innumerable suite, which he drags after him, excites the envy of all whom he meets. To fortune may be added power in the State, honours bestowed by the imperial throne, the government of a province, or the command of armies; a herald who precedes him is crying in a loud voice; lictors right and left also fill his subjects with awe, blows, confiscations, banishments, imprisonments, and all the means by which he strikes intolerable terror into all whom he has to rule. And what then? One night, a fever, a pleurisy, or an inflammation of the lungs, snatches away this man from the midst of men, stripped in a moment of all his stage accessories, and all this, his glory, is proved a mere dream. Therefore the Prophet has compared human glory to the weakest flower.
Source: Nine Homilies of Hexaemeron (New Advent)