3 Up to this point, the order in which plants shoot bears witness to their first arrangement. Every herb, every plant proceeds from a germ. If, like the couch-grass and the crocus, it throws out a shoot from its root and from this lower protuberance, it must always germinate and start outwards. If it proceeds from a seed, there is still, by necessity, first a germ, then the sprout, then green foliage, and finally the fruit which ripens upon a stalk hitherto dry and thick.
“Let the earth bring forth grass.” When the seed falls into the earth, which contains the right combination of heat and moisture, it swells and becomes porous, and, grasping the surrounding earth, attracts to itself all that is suitable for it and that has affinity to it. These particles of earth, however small they may be, as they fall and insinuate themselves into all the pores of the seed, broaden its bulk and make it send forth roots below, and shoot upwards, sending forth stalks no less numerous than the roots.
As the germ is always growing warm, the moisture, pumped up through the roots, and helped by the attraction of heat, draws a proper amount of nourishment from the soil, and distributes it to the stem, to the bark, to the husk, to the seed itself and to the beards with which it is armed. It is owing to these successive accretions that each plant attains its natural development, as well grain as vegetables, herbs or brushwood. A single plant, a blade of grass is sufficient to occupy all your intelligence in the contemplation of the skill which produced it. Why is the wheat stalk better with joints? Are they not like fastenings, which help it to bear easily the weight of the ear, when it is swollen with fruit and bends towards the earth?
Thus, while oats, which have no weight to bear at the top, are without these supports, nature has provided them for wheat. It has hidden the grain in a case, so that it may not be exposed to birds' pillage, and has furnished it with a rampart of barbs, which, like darts, protect it against the attacks of tiny creatures.
Source: Nine Homilies of Hexaemeron (New Advent)