Grasses are Nature's care. With these she clothes the earth; with these she sustains its inhabitants. Cattle feed upon their leaves; birds upon their smaller seeds; men upon the larger; for, few readers need be told that the plants which produce our bread-corn, belong to this class. In those tribes which are more generally considered as grasses, their extraordinary means and powers of preservation and increase, their hardiness, their almost unconquerable disposition to spread, their faculties of reviviscence, coincide with the intention of nature concerning them. They thrive under a treatment by which other plants are destroyed. The more their leaves are consumed, the more their roots increase. The more they are trampled upon, the thicker they grow. Many of the seemingly dry and dead leaves of grasses revive, and renew their verdure in the spring. In lofty mountains, where the summer heats are not sufficient to ripen the seeds, grasses abound which are viviparous, and consequently able to propagate themselves without seed. It is an observation, likewise, which has often been made, that herbivorous animals attach themselves to the leaves of grasses; and, if at liberty in their pastures to range and choose, leave untouched the straws which support the flowers.--_Paley._ [Verse: "For the earth bringeth forth fruit of herself; first the blade, then the ear, after that the full ear in the corn."--MARK V.] CHAPTER LX. 1167. _Why do some plants droop, and turn to the earth after sunset?_ Because, when the warmth of the son's rays is withdrawn, they turn downwards, and _receive the warmth of the earth by radiation_. 1167. _Why does the young ear of corn first appear enfolded in two green leaves?_ Because the light and air would _act too powerfully for the young ear_; two leaves therefore join, and embrace the ear, and protect it until it has acquired strength, when they divide, and leave the ear to swell and ripen. 1168. _Why are the seeds of plants usually formed within the corollas of flowers?_ Because the petals of the flowers, surrounding the seeds, _afford them protection until they are ripened_, when the flower dies, and the petals fall to the ground. 1169. _Why does the flower of the poppy turn down during the early formation of seed?_ Because the heat would probably be too great for the seed in its early stage. The plant is therefore provided with a curious _curve in its stalk_, which turns the flower downward. But when the seeds are prepared for ripening, _the stalk erects itself_, and the seeds are then presented to the ripening influences of the sun. 1170. _Why have plants of the pea tribe, a folding blossom called the "boat," or "keel?"_