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its body and leave some grains adhering to the stigma. The problem for the flower was how to attract the insect. If this end was secured less pollen need be produced, for less would be squandered; and the flower consequently began its self-adaptation to insect help by flattening out an outer ring of stamens, which supplied a resting-place and attracted attention by their hue. Yellow petals were probably the first allurement offered by plant to insect. There followed, in the struggle to obtain the services of insects, perfume and the secretion of sweet juices, and the modification of cells needed to produce these seems to have been accompanied sometimes by a change of colour in the petals, so that white flowers mark a somewhat higher
BEAN FLOWER stage in evolution than yellow ones.
However, small insects might visit a BEANS flower and feed on its juices without From "Stories of performing the services which these Plant Life,”
Bass (Heath) were intended to repay, and to keep out these undesirables some flowers barred the way to their nectar by a growth of hairs too dense for them to penetrate, or joined their petals into a long tube, at the bottom of which the nectar was concealed, obtainable only by a long-nosed insect such as a bee or a butterfly. More and more elaborate became the flower structure intended to preserve the sweet juices for the aristocracy of the insect world and at the same ne to render it impossible for them to take them without rendering the services for which they had been lured to come. The pea or bean flower, snapdragon, and monkshood are instances of flowers perfectly adapted to this end.
Changes of colour continued to accompany the perfecting of fertilization devices, and red, purple, and blue denote an ascending scale in the evolution of the flowering plants. Spots and lines of colour directing the insect to the nectar secretions-always placed so that it must do the desired work in taking them—also indicate that the flowers which have devised these short cuts to their ends are aristocrats of the plant world. Moreover, since it often happened that a bee or butterfly bearing
pollen on its body from one flower left some of it on the stigma of another of
the same species, METHOD OF DISTRIBUTION OF MILK
all the members of WEED SEEDS From “ Stories of Plant Life," Bass (Heath)
which told him by
their colour and markings that his visits in search of honey would not go unrewarded, and since the seeds produced by this cross-fertilization proved strongest and most likely to survive, most flowers as a further device to secure the continuance of their species arranged that their own pollen and the pistil should never be ripe at the same time, and trusted entirely to insects to carry out crossfertilization with another flower.
Having procured fertile seed, it remains for the parent plant to give them a satisfactory start in the world. They must if possible be prevented from merely dropping to the ground beneath, for in that case, stinted as they would be of air and light, they would have little chance of survival. To achieve their dispersal there are as many and as varied devices as those for bringing about fertilization. To assist transit by the wind many seeds are provided with inflated envelopes, or wings, or parachutes. When the seed reaches the ground the wings or parachutes either fall off, so that the seed shall not be carried on again, or if they remain fixed they do useful work by anchoring the seed to the ground so that it has a chance of germinating. When fruit-eating animals appeared, succulent cases for the seed, as in the gooseberry and cherry, bribed the animal to carry it away. Some fruits, such as nuts, try to escape attention by being green on the tree and turning brown when on the ground. The edible part in this case is the seed itself, and the problem for the plant is to thicken the shell so that it may resist the sharp teeth of squirrels and other nut-eating animals, and to disguise it so that it may escape notice. Other fruits and seeds are furnished with hooks by which they attach themselves to the feathers or rough coats of any bird or other animal that comes into contact with them. The animal usually carries them to some distance before it rids itself of them by rubbing.
An edible fruit is a reward offered to an animal for the dispersal of seeds. Edible seeds, however, such as coco-nuts, walnuts, acorns, peas, wheat, rice, barley, and many others, contain stores of food intended not for animals, but to give the young plant a start in life. The same is true of edible roots, potatoes, parsnips, and so on. Here, as in general, animals consume the food stores laid up by plants for their own use.
Plant life, it will be seen, is both subject to thinning by the attacks of animals and assisted by animals to multiply. When animal life evolved (destined as it was to obtain its food from plants) it must have seemed that plant life must perish before this new host of enemies. On the contrary, though the struggle for existence was made keener, the evolution of plants was assisted by this radical change in conditions. As has been seen, in the fertilization and dispersal of seeds animals could afford most valuable help. When, however, the plant had not immense powers of multiplying it was necessary to develop some protection for the green parts, without which plants cannot live, against the attacks of animals, who are often driven by hunger to seek food even at the cost of destroying their own means of subsistence. It is only man who protects the plants to conserve his future food stores. With this end in view some plants developed spines and prickles upon those parts within reach of grazing animals; trees produced a tough bark; shrubs, such as rhododendrons; indigestible tissues. The stinging nettle evolved a defence, and some sense told the animals that hemlock, henbane, monkshood, and many other plants were poisonous to eat.
In these and similar ways the plants held their ground, and even, in situations exceptionally favourable to them, as in tropical forests, were able to put animal life at a great disadvantage. On the whole, plant and animal life progressed side by side, animal life dependent on plant life and preying upon it, yet at the same time rendering it services which enabled the plants to hold their own.
EVOLUTION OF ANIMAL LIFE-THE LOWER
NIMAL life, like plant life, began on water, and
advanced from simple forms to forms more
highly organized. We cannot, as has been said in the case of plants, expect to find a perfect record of their evolution in the rocks. Some animals had no structure that could survive in fossil form; others left their bones in rock unsuitable for their preservation ; the rocks themselves in many instances have been unmade and remade time after time. As Darwin says: “We must look at the geological record as a history of the world imperfectly kept.” We have, however, certain fossil series showing the development, and sometimes the disappearance, of animal types; we have a wonderful number of types preserved ; and we have evidence in the age of the rocks in which their remains are preserved that higher and higher groups of animals appear in successive periods of the earth's history. Backboneless animals make their appearance before backboned. Backbones are developed first in fish. Two geological epochs later-by which vast stretches of time must be understood-we find the first amphibians—that is, animals successively at home both in water and on land ; and this is momentous, since it marks the fact that animals destined for a life in water have succeeded by adaptation of structure in accommodating themselves to life on dry land. Two elements