3. PLANT MEN AND OTHERS
Before passing on to tell the story of our galaxy as a whole (so far as I can comprehend it) I must mention another and a very alien kind of world. Of this type we found few examples, and few of these survived into the time when the galactic drama was at its height; but one at least had (or will have) a great influence on the growth of the spirit in that dramatic era.
On certain small planets, drenched with light and heat from a near or a great sun, evolution took a very different course from that with which we are familiar. The vegetable and animal functions were not separated into distinct organic types. Every organism was at once animal and vegetable.
In such worlds the higher organisms were something like gigantic and mobile herbs; but the violent flood of solar radiation rendered the tempo of their life much more rapid than that of our plants. To say that they looked like herbs is perhaps misleading, for they looked equally like animals. They had a definite number of limbs and a definite form of body; but all their skin was green, or streaked with green, and they bore here or there, according to their species, great masses of foliage. Owing to the slight power of gravitation on these small planets, the plant-animals often supported vast super-structures on very slender trunks or limbs. In general those that were mobile were less generously equipped with leaves than those that were more or less sedentary.
In these small hot worlds the turbulent circulation of water and atmosphere caused rapid changes in the condition of the ground from day to day. Storm and flood made it very desirable for the organisms of these worlds to be able to move from place to place. Consequently the early plants, which owing to the wealth of solar radiation could easily store themselves with energy for a life of moderate muscular activity, developed powers of perception and locomotion. Vegetable eyes and ears, vegetable organs of taste, scent and touch, appeared on their stems or foliage. For locomotion, some of them simply withdrew their primitive roots from the ground and crept hither and thither with a kind of caterpillar action. Some spread their foliage and drifted on the wind. From these in the course of ages arose true fliers. Meanwhile the pedestrian species turned some of their roots into muscular legs, four or six, or centipedal. The remaining roots were equipped with boring instruments, which on a new site could rapidly proliferate into the ground. Yet another method of combining locomotion and roots was perhaps more remarkable. The aerial portion of the organism would detach itself from its embedded roots, and wander off by land or air to strike root afresh in virgin soil. When the second site was exhausted the creature would either go off in search of a third, and so on, or return to its original bed, which by now might have recovered fertility. There, it would attach itself once more to its old dormant roots and wake them into new activity.
Many species, of course, developed predatory habits, and special organs of offense, such as muscular boughs as strong as pythons for constriction, or talons, horns, and formidable serrated pincers. In these "carnivorous" creatures the spread of foliage was greatly reduced, and all the leaves could be tucked snugly away along the back. In the most specialized beasts of prey the foliage was atrophied and had only decorative value. It was surprising to see how the environment imposed on these alien creatures forms suggestive of our tigers and wolves. And it was interesting, too, to note bow excessive specialization and excessive adaptation to offense or defense ruined species after species; and how, when at length "human" intelligence appeared, it was achieved by an unimposing and inoffensive creature whose sole gifts were intelligence and sensibility toward the material world and toward its fellows. Before describing the efflorescence of "humanity" in this kind of world I must mention one grave problem which faces the evolving life of all small planets, often at an early stage. This problem we had already come across on the Other Earth. Owing to the weakness of gravitation and the disturbing heat of the sun, the molecules of the atmosphere very easily escape into space. Most small worlds, of course, lose all their air and water long before life can reach the "human" stage, sometimes even before it can establish itself at all. Others, less small, may be thoroughly equipped with atmosphere in their early phases, but at a much later date, owing to the slow but steady contraction of their orbits, they may become so heated that they can no longer hold down the furiously agitated molecules of their atmosphere. On some of these planets a great population of living forms develops in early aeons only to be parched and suffocated out of existence through the long-drawn denudation and desiccation of the planet. But in more favorable cases life is able to adapt itself progressively to the increasingly severe conditions. In some worlds, for instance, a biological mechanism appeared by which the remaining atmosphere was imprisoned within a powerful electromagnetic field generated by the world's living population. In others the need of atmosphere was done away with altogether; photosynthesis and the whole metabolism of life were carried on by means of liquids alone. The last dwindling gases were captured in solution, stored in huge tracts of spongy growths among the crowded roots, and covered with an impervious membrane.
Both these natural biological methods occurred in one or other of the plant-animal worlds that reached the "human" level. I have space only to describe a single example, the most significant of these remarkable worlds. This was one in which all free atmosphere had been lost long before the appearance of intelligence.
To enter this world and experience it through the alien senses and alien temperament of its natives was an adventure in some ways more bewildering than any of our earlier explorations. Owing to the complete absence of atmosphere, the sky, even in full sunlight, was black with the blackness of interstellar space; and the stars blazed. Owing to the weakness of gravitation and the absence of the molding action of air and water and frost on the planet's shrinking and wrinkled surface, the landscape was a mass of fold-mountains, primeval and extinct volcanoes, congealed floods and humps of lava, and craters left by the impact of giant meteors. None of these features had ever been much smoothed by atmospheric and glacial influences. Further, the ever-changing stresses of the planet's crust had shattered many of the mountains into the fantastic forms of ice-bergs. On our own earth, where gravity, that tireless hound, pulls down its quarry with so much greater strength, these slender, top-heavy crags and pinnacles could never have stood. Owing to the absence of atmosphere the exposed surfaces of the rock were blindingly illuminated; the crevasses and all the shadows were black as night.
Many of the valleys had been turned into reservoirs, seemingly of milk; for the surfaces of these lakes were covered with a deep layer of a white glutinous substance, to prevent loss by evaporation. Round about clustered the roots of the strange people of this world, like tree-stumps where a forest has been felled and cleared. Each stump was sealed with the white glue. Every stretch of soil was in use; and we learned that, though some of this soil was the natural result of past ages of action by air and water, most was artificial. It had been manufactured by great mining and pulverizing processes. In primitive times, and indeed throughout all "pre-human" evolution, the competitive struggle for a share of the rare soil of this world of rock had been one of the main spurs to intelligence.
The mobile plant-men themselves were to be seen by day clustered in the valleys, their foliage spread to the sun. Only by night did we observe them in action, moving over the bare rock or busy with machines and other artificial objects, instruments of their civilization. There were no buildings, no roofed weatherproof enclosures; for there was no weather. But the plateaux and terraces of the rock were crowded with all manner of artifacts unintelligible to us.