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Because, when the warmth of the son's rays is withdrawn, they turn downwards, and receive the warmth of the earth by radiation.1167.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?"

Because, within that blossom the pea is formed, and the shape of the blossom is exactly suited to that of the pea which is formed therein. The blossom is itself protected by external petals; and when the wind blows, and threatens to destroy the parts upon which the seeds depend, the plants turn their backs to the wind, and shelter the seed.

"The fruit of the righteous is a tree of life; and he that winneth souls is wise."—Proverbs xi.

1171. Why are the leaf buds enclosed in scales which fall off as the leaf opens?

Because the scales serve as a shelter to the tender structure of the young leaf. The scales are rudimentary leaves, formed at the end of the previous season, and which, being undeveloped then, serve to guard the young leaves of the future year.

In trees, especially those which are natives of colder climates, this point is taken up earlier. Many of these trees (observe in particular the ash and the horse-chestnut) produce the embryos of the leaves and flowers in one year, and bring them to perfection the following. There is a winter therefore to be gotten over. Now what we are to remark is, how nature has prepared for the trials and severities of that season. These tender embryos are, in the first place wrapped up with a compactness, which no art can imitate; in which state they compose what we call the bud. This is not all. The bud itself is enclosed in scales; which scales are formed from the remains of past leaves, and the rudiments of future ones. Neither is this the whole. In the coldest climates, a third preservative is added, by the bud having a coat of gum or resin, which, being congealed, resists the strongest frosts. On the approach of warm weather this gum is softened, and ceases to be an hindrance to the expansion of the leaves and flowers. All this care is part of that system of provisions which has for its object and consummation, the production and perfecting of the seeds.—Paley.1172. Why are the seeds of many plants enclosed in a rich juice, or pulp?

Because the matter by which the seed is surrounded, as well as being intended for the nourishment and care of the seed, is designed for the use of man and of animals, by whom the seed is set free to take its place in the earth.

By virtue of this process, so necessary, but so diversified, we have the seed, at length, in stone-fruits and nuts, incased in a strong shell, the shell itself enclosed in a pulp or husk, by which the seed within is, or hath been, fed; or, more generally (as in grapes, oranges, and the numerous kinds of berries), plunged overhead in a glutinous syrup, contained within a skin or bladder; at other times (as in apples and pears) embedded in the heart of a firm fleshy substance; or (as in strawberries) pricked into the surface of a soft pulp.

These and many more varieties exist in what we call fruits. In pulse, and grain, and grasses; seeds (as in the pea tribe) regularly disposed in parchment pods, which, though soft and membranous, completely exclude the wet even in the heaviest rains; the pod also, not seldom, (as in the bean), lined with a fine down; at other times (as in the senna) distended like a blown bladder; or we have the seed enveloped in wool (as in the cotton-plant), lodged (as in pines) between the hard and compact scales of a cone, or barricadoed (as in the artichoke and thistle) with spikes and prickles; in mushrooms, placed under a pent-house; in ferns, within slits in the back part of the leaf; or (which is the most general organisation of all) we find them covered by strong, close tunicles, and attached to the stem according to an order appropriated to each plant, as is seen in the several kinds of grains and of grasses.

"And I will send grass in thy fields for thy cattle, that thou mayest eat, and be full."—Deuteronomy xi.

In which enumeration, what we have first to notice is, unity of purpose under variety of expedients. Nothing can be more single than the design; more diversified than the means. Pellicles, shells, pulps, pods, husks, skin, scales armed with thorns, are all employed in prosecuting the same intention. Secondly; we may observe, that in all these cases, the purpose is fulfilled within a just and limited degree. We can perceive, that if the seeds of plants were more strongly guarded than they are, their greater security would interfere with other uses. Many species of animals would suffer, and many perish, if they could not obtain access to them. The plant would overrun the soil; or the seed be wasted for want of room to sow itself. It is, sometimes, as necessary to destroy particular species of plants, as it is, at other times, to encourage their growth. Here, as in many cases, a balance is to be maintained between opposite uses. The provisions for the presentation of seeds appear to be directed, chiefly against the inconstancy of the elements, or the sweeping destruction of inclement seasons. The depredation of animals, and the injuries of accidental violence, are allowed for in the abundance of the increase. The result is, that out of the many thousand different plants which cover the earth, not a single species, perhaps, has been lost since the creation.

When nature has perfected her seeds, her next care is to disperse them. The seed cannot answer its purpose, while it remains confined in the capsule. After the seeds therefore are ripened, the pericarpium opens to let them out, and the opening is not like an accidental bursting, but for the most part, is according to a certain rule in each plant. What I have always thought very extraordinary; nuts and shells, which we can hardly crack with our teeth, divide and make way for the little tender sprout which proceeds from the kernel. Handling the nut, I could hardly conceive how the plantule was ever to get out of it. There are cases, it is said, in which the seed-vessel, by an elastic jerk, at the moment of its explosion, casts the seeds to a distance. We all, however, know, that many seeds (those of most composite flowers, as of the thistle, dandelion, &c.) are endowed with what are not improperly called wings; that is, downy appendages, by which they are enabled to float in the air, and are carried oftentimes by the wind to great distances from the plant which produces them. It is the swelling also of this downy tuft within the seed-vessel that seems to overcome the resistance of its coats, and to open a passage for the seed to escape.

But the constitution of seeds is still more admirable than either their preservation or their dispersion. In the body of the seed of every species of plant, or nearly of every one, provision is made for two grand purposes: first, for the safety of the germ; secondly, for the temporary support of the future plant. The sprout, as folded up in the seed, is delicate and brittle beyond any other substance. It cannot be touched without being broken.

Yet in beans, peas, grass-seeds, grain, fruits, it is so fenced on all sides, so shut up and protected, that whilst the seed itself is rudely handled, tossed into sacks, shovelled into heaps, the sacred particle, the miniature plant remains unhurt. It is wonderful, also, how long many kinds of seeds, by the help of their integuments, and perhaps of their oils, stand out against decay. A grain of mustard-seed has been known to lie in the earth for a hundred years; and as soon as it had acquired a favourable situation, to shoot as vigorously as if just gathered from the plant. Then, as to the second point, the temporary support of the future plant, the matter stands thus. In grain, and pulse, and kernels, and pipins, the germ composes a very small part of the seed. The rest consists of a nutritious substance, from which the sprout draws its aliment for some considerable time after it is put forth; viz., until the fibres, shot out from the other end of the seed, are able to imbibe juices from the earth, in a sufficient quantity for its demand. It is owing to this constitution that we see seeds sprout, and the sprouts make a considerable progress, without any earth at all.

"Say not ye, There are four months, and then cometh harvest? behold, I say unto you, Lift up your eyes, and look on the fields; for they are white already to harvest."—John iv.

From the conformation of fruits alone, one might be led, even without experience, to suppose, that part of this provision was destined for the utilities of animals. As limited to the plant, the provision itself seems to go beyond its object. The flesh of an apple, the pulp of an orange, the meat of a plum, the fatness of the olive, appear to be more than sufficient for the nourishing of the seed or kernel. The event shows, that this redundancy, if it be one, ministers to the support and gratification of animal natures; and when we observe a provision to be more than sufficient for one purpose, yet wanted for another purpose, it is not unfair to conclude that both purposes were contemplated together.—Paley.1173. Why have climbing plants tough curly tendrils?

Because, having no woody stalks of their own to support them, they require to take hold of surrounding objects, and raise themselves from the ground by climbing. Their spiral tendrils are, therefore, so many hands, assisting them to rise from the earth.1174. Why does the pea put forth tendrils, and the bean not?

Because the bean has in its stalk sufficient woody fibre to support itself, but the pea has not. We do not know a single tree or shrub having a firm strong stem sufficient for its support which is also supplied with tendrils.1175. Why do the ears of wheat stand up by day, and turn down by night?

Because, when the ear is becoming ripe, the cold dew falling into the ear, might induce blight; the ears therefore turn down to the earth, and receive warmth by radiation.1176. Why have grasses, corn, canes, &c., joints, or knots in their stalks?

Because a long hollow stem would be liable to bend and break. But the joints are so many points where the fibres are bound together, and the structure greatly strengthened.

"Then shall the earth yield her increase; and God, even our own God, shall bless us."—Psalm xlvii.

1177. Why have the berries of the mistletoe a thick viscid juice?

Because the mistletoe is a parasitical plant, growing upon the bark of other trees. It will not grow in the ground; its seeds are therefore filled with an exceedingly sticky substance, which serves to attach them to the bark of trees, to which the berries attach themselves at once, by throwing out tough fibres; and the next year the plant grows.

1178. How are the seeds of the mistletoe transferred from its own stem to the bark of trees?

Various birds, and particularly the missel thrush, feed upon the berries. As the bird moves in pursuit of its food, the viscid berries attach themselves to its feathers, and in this way the thrush is the instrument which conveys the seed to the spot to which it adheres, and from which the tree ultimately grows.1179. What is the circulation of the sap in plants?

The circulation of the sap is the movement of the nutritive juices by which the plant is sustained. There is a slow uninterrupted movement of the sap from the root through the stems to the leaves, and downwards from the leaves through the bark to the root.

"For the sun is no sooner arisen with a burning heat, but it withereth the grass, and the flower thereof falleth, and the grace of the fashion of it perisheth: so also shall the rich man fade away in his ways."—James i.

1180. Why does the sap of plants thus ascend and descend?

Because it conveys upward from the ground some of the matter by which the plant is to be nourished, and which must undergo digestion in the leaves; and it brings downward from the leaves the matters absorbed, for the nourishment of the plant, and discharges through the root the substances which the plant cannot use.

The movement of the sap is most active in the spring; but in the depths of the winter it almost ceases.

There are other motions of the sap in plants, which are called special, in distinction from the ascending and descending of the sap, which is called general, or common to all plants. The special movements of the sap are peculiar to certain plants, in some of which a fluid, full of little green cells, is found to have a rotatory motion; in other plants, a milky fluid is found to move through particular tissues of the vegetable structure.1181. Why are the leaves of plants green?

Because they secrete a carbonaceous matter, named chlorophyll, from which they derive their green colour.1182. Why are the hearts of cabbages, lettuces, &c., of a pale yellow colour?

Because the action of light is necessary to the formation of chlorophyll; and as the leaves are folded upon each other, they exclude the light, and the green matter is not formed.1183. Why do leaves turn brown in the autumn?

Because, when their power of decomposing the air declines, the oxygen absorbed in the carbonic acid gas, lodges in the leaf, imparting to it a red or brown colour.1184. Why do succulent fruits, such as gooseberries, plums, &c., taste acid?

Because, in the formation of juices, a considerable amount of oxygen is absorbed, and the oxygen imparts acidity to the taste.

"The earth is full of the goodness of the Lord."—Psalm xxxiii.

1185. Why do ripe fruits taste sweet, and unripe fruits taste sour?

Because the juices of the ripe fruit contain a large proportion of sugar, which in the unripe fruit has not been formed.1186. Why do some leaves turn yellow?

Because they retain an excess of nitrogen. Leaves undergoing decay turn either yellow, red, crimson, or violet. Yellow is due to the excess of nitrogen; red and crimson to various proportions of oxygen; violet to a mixture of carbon; and green to chlorophyll.1187. Why do leaves fall off in the autumn?

Because they have supplied for a season the natural wants of the tree. Every part has received nutrition through the spring and summer months; and the wants of the tree being supplied, the chief use of the leaf ceases, and it falls to the ground to decay, and enrich the soil.1188. Why do plants suffer from the smoke of cities?

Because the smoke injures the porous structure of the leaves, and interferes with their free respiration.