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plant-matter under proper conditions of moisture and temperature. In this we see that living matter somehow can resist most of them while dead matter cannot. Plants suffer from them as well as animals, and by this means we have been able to isolate a number of chemical products by which immunity is evidently maintained. It is a quite remarkable fact that where large numbers of related orders of plant life are highly protected they are among the oldest and least specialized forms. Recently evolved, highly specialized forms, when thus protected from pathogenetic organisms of great virulence, usually stand alone among their kindred, none of which are thus gifted. This would seem to indicate that at an early period the danger of invasion was greater, and that with the advance of time their attacks were less marked over the world at large, but equally well marked in special regions. This singular condition is observed in the Gymnosperms, where scarcely a species exists that is not charged with turpentine and antiseptic resin. It could have been no local necessity that evolved so general a characteristic. Going higher up, we observe the willows and their salicin. Here we see a less general endowment, and note the fact that their swampy habitat may account for their possessing this means of protection. With the still more highly specialized Cinchonas we have a very remarkable case. The environment, too, casts a flood of light upon its significance, and the narrow range of the protected species confirms the belief that local and not general conditions evolved it. The native home of these trees is on the Andean slopes in South America, not far from the Equator. Their habitat is a region of perpetual fog and drizzle. For nine months of the year scarcely a ray of direct sunlight reaches them, and during the other three there is a chasing of clouds and sunshine hour by hour during the day, much like our April weather. It is an ideal home of malaria, unfit for human habitation. In those years when the fogs are densest and the sunshine least, the yield of quinine from the bark is known to be greatest. What other conceivable function can this quinine serve the tree than as a destroyer of malaria germs? It is only found in abundance in the parts of

the tree likely to be subject to their attacks. It multiplies under the very conditions that multiply the germs, and that would therefore make them more dangerous to the plant. The home of the tree is the natural home of such germs. In India, where Cinchona is now artificially cultivated they cover the bark of the growing trees with cotton and shield them from direct sunlight the year when they are going to strip them, having found experimentally that this treatment increases the quinine yield very markedly. Before they adopted this plan the yield was discouragingly small and becoming smaller. Now it compares favorably with that from wild trees in South America. By such treatment they imitate in a measure the conditions of their original homes, and the very conditions that indicate danger from germs to the tree. The tree has the power of anticipating such danger and guarding against it. The condition of the Cinchona belt on the Andean slope we have reason to think was the condition of most of the earth during that period of its history when Gymnosperms were the chief forms of plants. As a consequence, the protection instead of being confined to a single species, genera, or even order, covers a vast range of orders.

If the air by its buoyancy floats disease germs and enables them to kill off the weak and make room for the strong, it likewise floats the pollen of millions of plants and thereby aids healthy fertilization. Experiments made by Charles Darwin and others have shown that when plants fertilize themselves, or when fertilization is confined to close of kin, deterioration results. The intermarriage of plants of the same species raised at points remote from each other, and from seed without kinship, leads on the other hand to increase in vigor. Without cross-fertilization there is retrogression instead of progression, and therefore nature has adopted some of the most curious and remarkable methods of avoiding self-fertilization. The wind is, directly or indirectly, the marriage priest of nearly every plant on the earth. Sometimes it bears the pollen from enormous distances as in the case of the palms in Palermo, Italy, that were fertilized by others of their kind in Africa. Farmers who wish to grow

sorghum when their neighbors are growing broomcorn, or vice versa, know well the power of the wind in spoiling their crops by this carrying of pollen. But while, in such an instance, cross-fertilization works mischief, the rule is the reverse. It has beautified the earth by leading to all the brilliancy of our finest floral displays.

The successive steps of change from wind-fertilization to insect-fertilization were all made possible by the air. Every insect and every little humming-bird that acts as a pollen-carrier to lilies and rhododen drons, kalmias and sweet peas, roses and foxgloves can only fly by virtue of the air's support. The development of these lovely forms and brilliant colors could not have occurred but for this buoyant power of the air. It also carries the rich fragrance that at twilight hour guides and allures moths and butterflies to brightcolored and especially to white flowers. The recipro cal action of flowers on insects is equally important in this connection. Only such insects as were able to fertilize the flowers by virtue of their forms and sizes could make a living and survive. Through countless generations each each has fixed a line of conduct for the other, failure to pursue which meant death. Nature's changes are usually fair exchanges. She leaves no permanent place for dishonesty. When the wild bees of the Tyrolese Alps pierce the bases of the aconite flowers and steal the honey without rendering a return in service by carrying pollen to the stigmas, the penalty is paid in a succeeding year by starvation. Such inordinate haste to become rich on their part produces a dearth of aconite in succeeding years. No fertilization, no seeds; no seeds, no plants, no plants, no honey, and no honey, no bees. Here again we see that all suffer together, and that the moral lapses of others are charged to the account of the whole community. We are our brothers' keepers. Nature does not consider individuals in her reckonings as much as she does whole races. Like the signers of the Declaration of Independence, "we must all hang together or we will hang separate."

The power that birds and insects possess of flying could not have become developed in a more appro

priate time than when it did. The first efforts at fly.. ing among vertebrates were accomplished by bat-like creatures with leather wings. The pterodactyls were good illustrations of these primitive predecessors of our birds. Feathers came as an after growth. It is probable that the first wings of insects were relatively of equal coarseness and crudity. It is quite likely that they appeared as an adjunct to an exaggerated jumping power. Their clumsy and awkward efforts were fortunately favored by a very dense atmosphere. Had they now to acquire such power the chances are that natural selection would wipe them all out before a favored pair appeared.

With the progressive rarification of the air, birds kept pace by evolving hollow feathers and light down, while insects' wings thinned themselves out to lightest gossamer. Of the unnumbered millions swept away because they did not or could not so change, we have no record. We only keep account of Nature's successes. We know, however, that every step of progress came by selecting those with favorable qualities and dis couraging or destroying those with unfavorable ones. None ever came by trying to change lions into lambs, or thistles into roses. Even the most insignificant characteristics cannot be altered and maintained in that way so far as science has yet demonstrated.

To the density of the atmosphere, human beings, and the higher animals also, owe much of their progress. But for it, our upright attitude could not have been maintained by any such mechanism as the present ball and socket arrangement of our thigh bones. These bones are held in their places mainly by the pressure of the atmosphere. The strength of our mucous membranes and possibly also of the outer cuticles is accurately adjusted to the terrestrial limits of this force. Our eyes, too, are under control of its balances. rapidly remove the present atmospheric pressure from any animal is to cause its death, not by absence of oxygen, but from mechanical injuries to the tissues. The slow removal of the pressure permits us within a limited range to acquire new adjustments of the bal ance that save us from injury; but if we transcend those limits the results are disastrous.



in making high ascents in their balloons, find that on passing a certain height their ears, noses, lips and eyes begin to bleed spontaneously. With some, this bleeding comes on at lower altitudes than others, and there are people so susceptible to this trouble that they cannot live in regions above the sea level. Such people are known among medical men as bleeders. Having been evolved in the midst of a definite range of pressure we are only adapted to live within such conditions, and must suffer when we undertake to transcend them. As in the case of resisting certain forms of bacterial attack, so also in resisting changes in atmospheric pressure our powers vary with our strength. The workings of our internal organs are adjusted to definite pressures and these in diseased conditions of the same are exceedingly sensitive to the slightest changes in this particular. Minute barometric alterations profoundly influence the very sick. The rhythm of exacerbation and improvement often follows the ups and downs of the mercury as the compassneedle follows the direction of the pole. Then again what we call good and bad weather have decidedly marked effects on the sick, and changes in the weather result from variations in the pressure of the atmosphere. Cold weather and hot weather, wet weather and dry weather, foggy weather and clear weather, calm weather and windy weather are all products of variations in the pressure of the atmosphere. Every one of these special kinds of weather brings upon the community special types of disease and carries off the sick where but for their advent the physician's skill would have saved the patients. The Encyclopædia Britannica sums this up as follows: "The curves show that the maximum annual mortality from the different diseases groups around certain specific conditions of temperature and moisture combined. Thus, cold and moist weather is accompanied by a high death rate from heart disease, diphtheria and measles; cold weather, with a high death rate from bronchitis, pneumonia, rheumatism, etc.; cold and dry weather, with a high death rate from suicide and smallpox; hot weather with a high death rate from bowel complaints; and warm moist weather, with a high death rate from scarlet and typhoid fevers."

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