Part 7

Some very striking adaptations of form of organs to the intensity of the light have been analyzed by Goebel. The common harebell (_Campanula rotundifolia_) has an upright stem twenty to sixty centimetres in height. The upper part of the stem bears sessile lanceolate leaves, decreasing in size from the base to the summit. The first leaves formed by the stem on its emergence from the soil are entirely different in construction, showing a heart-shaped lamina with a distinct petiole. These leaves are formed at the actual surface of the soil, are generally more or less shaded or covered by fallen leaves, and in fact are not known or seen by many collectors or observers of the plant. Goebel found that similar leaves might be formed on any part of the plant if it were shaded from the full glare of the sun's rays. The cordate leaves at the base of the stem were always produced, however, no matter to what intensity of illumination that part of the plant was subjected. It is therefore safe to conclude that the cordate leaves are inherited forms, and that the lanceolate organs are adaptations to light which may be shown by any individual of the species.

In general it is to be said that the leaves of sun-loving species have a thick epidermis, entirely free from chlorophyll, with stomata on the lower side only, a firm consistence due to the formation of woody tissues, and are often provided with a coating of hairs. The leaves of shade-loving plants, on the other hand, have a thin-walled epidermis often containing chlorophyll, stomata on both sides, and are not so plentifully provided with hairs as those in exposed situations.

The variations in external form described above are due to the intensity of the illumination. At the same time the structure and arrangement of the cells depend on the direction from which the light rays come. Thus, an organ receiving light from one side only will exhibit a structure different from an organ of the same kind receiving direct rays from two or more sides. Light, then, is a cause of dorsiventrality--that is, of the fact that the upper and lower sides of organs are not alike in structure. The leaf affords a splendid example of dorsiventrality as a result of the exposure of one side only to direct light. The upper side of a horizontal leaf, such as the oak, beech, or maple, contains one or two layers of cylindrical cells with their long axes perpendicular to the surface. In vertical leaves, such as the iris, these _palisade_ cells, as they are termed, are not so well defined, and in all leaves grown in darkness this tissue is very much reduced. If a young leaf not yet unfolded from the bud is fastened in such a position that the under side is uppermost, palisade cells will be formed on the side exposed to the direct rays of the sun.

The influence of light upon the sporophylls, or reproductive organs of the seed-forming plants, is quite as well defined as upon the vegetative organs.

In general it is to be said that stamens and pistils may reach functional maturity in darkness or diffuse light, and if pollination is provided for, seed and fruit formation may ensue.

The diminution of light has the effect of transforming inflorescences into leafy shoots in some instances, however. The more common reaction consists of alterations in the size, form, and color of the perianth, and greater changes are induced in the petals than in the sepals. The corolla shows greater decrease in size in _Melandryum_ and _Silene_, in diffuse light, though the relative form is maintained. The writer has obtained most striking results from growing flowers of _Salvia_ (sage) in a dark chamber, inclosing the inflorescence only. In the normal flower the irregular scarlet corolla attains three times the length of the calyx, and two stamens extrude from under the upper lip. When grown in darkness, the corolla with the adherent stamens measure about three millimetres in length, or one twelfth the normal, and are scarcely more than half the size of the calyx, which is but two thirds the size of similar organs grown in the light. The color is entirely lacking from the corolla, and is found only along the veins of the calyx.

In other instances in which the corolla is composed of separate members, an unequal reaction is exhibited. The corolla of nasturtium (_Tropæolum majus_) consists of five approximately equal petals. Flowers of this species grown in darkness show one of nearly normal stature, two of reduced size, while the remaining two take the form of club-shaped bracts.

The diminished size of the perianth of cleistogamous flowers of such types as the violet is due directly to the action of diminished light upon the hidden or inclosed flower.

The influence of light upon the structure, reproductive processes, and distribution of the lower forms brings about the most widely divergent reactions, which can not be described here.

The distribution and color of marine algæ depend upon the depth of the water and the consequent intensity of the light. This gives rise to distinct zones of aquatic vegetation. Thus in one series of surveys the _littoral_ zone, the beach area covered at high water and exposed at low water, was found to furnish proper conditions for green, brown, and red algæ. The _sublittoral_ zone, extending to a depth of forty metres, is furnished with red algæ, increasing in number with the depth, and the brown algæ disappear; while the _elittoral_ zone, from forty to one hundred and ten metres, is inhabited by red algæ alone. The number of species of vegetal organisms below this depth is extremely small. An alga (_Halosphæria viridis_) has been brought up from depths of one thousand to two thousand metres.

A very great number of bacteria are unfavorably affected by light, and find proper conditions at some depth in the soil or water. It is on account of this fact that the water of frozen streams becomes more thickly inhabited by certain organisms than in the summer time, and exposure to sunlight is adopted as a hygienic measure in freeing clothing and household effects from infection. Bacteria occur abundantly in sea water at depths of two hundred to four hundred metres, and quite a number of species are to be found at eight hundred to eleven hundred metres.

The distribution of fungi follows the general habit of bacteria in that they thrive best in darkness.

It is to be noticed in this connection that light is also a determining factor in the distribution of the higher land plants. Thus the amount of light received in polar latitudes is quite insufficient for the needs of many species, entirely irrespective of temperature.

The retarding influence of light upon growth is even more marked in the lower forms than in the higher. Such action is the result of the disintegrating effect of the blue-violet rays upon ferments and nitrogenous plastic substances.

The greater massiveness of the bodies of the higher plants enables them to carry on the chemical activities in which these substances are concerned in the interior, where the intense rays may not penetrate. The attenuated and undifferentiated fungi must seek the shade, to escape the dangers of strong light, against which they have no shield.

The reproductive processes are particularly sensitive to illumination. The formation of zoöspores by green felt (_Vaucheria_) may occur only in darkness, at night, or in diffuse light, and these examples might be multiplied indefinitely. Many features of the germination of spores and the growth of _protonemæ_ or _prothallia_ among the mosses, liverworts, and ferns are determined by light.

Perhaps the most striking reactions of plants to light are to be seen in locomotor and orientation movements.

Locomotor movements are chiefly confined to lower forms, and are most noticeable in the "swarm spores," or zoöspores of the algæ, though exhibited by spermatozoöids as well. Zoöspores may be seen collected against the side of the vessel receiving direct sunlight, while the opposite side of the vessel will be free from them. The chlorophyll bodies of green cells arrange themselves similarly. The latter bodies may move away from the exposed side of the cell if the light exceeds a certain intensity.

The typical plant may not move its body toward or away from the source of light, but it may secure the same end by dispositions of its surfaces to vary the angle at which the rays are received. This form of irritability is one of the most highly developed properties of the plant. Wiesner has found that a seedling of the vetch is sensitive to an amount of light represented by one ten-millionth of a unit represented by a Roscoe-Bunsen flame. The "sensitiveness" to light may take one of three forms: The organ may place its axis parallel and pointing toward the source of the rays, as in stems, when it is said to be _proheliotropic_; the axis of the organ may assume a position perpendicular to the rays, which is designated as _diaheliotropism_; or it may place its axis parallel to the rays and pointing away from the light, when it is said to be _apheliotropic_. Upright stems are proheliotropic, horizontal leaves and creeping stems are diaheliotropic, and roots and such stems as those of ivy are apheliotropic.

Sunlight varies from zero to the full blaze of the noonday sun, and assumes its greatest intensity in the equatorial regions. The intensity in latitudes 40° to 45° north would be represented by 1.5 units, and at the equator by 1.6 units. Near the equator the intensity is so great that an ordinary leaf may not receive the full force of the noonday sun without damage. The injury would not result from the luminous rays, but from the temperatures, 40° to 50° C., arising from the conversion of light into heat. As an adaptation to this condition nearly all leaves have either a pendent or a vertical position, or the power of assuming this position by motor or impassive wilting movements.

Among the plants of the temperate zone the so-called compass plants are examples of similar adaptations. The compass plants include, among others, the wild lettuce (_Lactuca scariola_) and rosin weed (_Silphium laciniatum_). These plants place the leaves in a vertical position with the tips pointing north and south in such manner that the direct rays of the morning and evening sun only may strike the surfaces at right angles, while the edges are presented to the fierce rays at noonday. That this arrangement is an adaptation against the intense light is evident when it is seen that specimens growing in shaded locations or in diffuse light place the leaves in the typical horizontal position. To meet the functional conditions, both sides of the compass leaves are almost equally provided with palisade cells for food formation and stomata for transpiration. The estimation of the light striking a compass leaf shows that it receives approximately the same amount of light as a horizontal leaf during the course of a day, but the two maxima of intensity, morning and evening, are much below that of the noon of horizontal leaves.

The influence of light upon plants may be briefly summed as follows:

Light is necessary for the formation of food substances by green plants, and it is an important factor in distribution in land and marine forms.

Growth and reproduction are generally retarded by the action of the blue-violet rays.

Light is fatal to certain bacteria and other low forms of vegetable life.

Many plants have the power of accelerated growth of stems in diminished light as an adaptation for lifting the leaves above "shading" objects.

The growth of many leaves and of the perianth of flowers is hindered in diminished light.

The outward form of many organs, particularly leaves, is dependent upon the intensity of the light received.

The internal structure of bilateral or dorsiventral organs is largely determined by the direction of the rays.

Plants have the power of movement to adjust their surfaces to a proper angle with impinging light rays, as a protective adaptation.

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THE STONE AGE IN EGYPT.

BY J. DE MORGAN.

The investigation of the origin of man in Egypt is a very complex problem, belonging as much to geology as to archæology. The earliest evidences we have of human industry, in fact, go back to so remote a period that they should be regarded rather as fossils than as archæological documents. They are very coarsely worked flints, which are found near the surface of the ground among the pebbles of the Quaternary or Pleistocene epoch, and similar to those which occur abundantly in Europe, America, and Asia; but the study and collection of them have been pursued with less method than in those countries. The more recent monuments, so much more conspicuous and more easily accessible, have attracted most attention, while these have been left in the background.

No region in the world presents a clearer and more distinct individual character than Egypt. Each village is a special world, each valley a universe that has developed its own life; and man has felt the special local impressions; and even in modern times, while all the Egyptian villages present a similar aspect, and although the fellah appears to be the same sort of a man everywhere, each locality has its special individual characteristics. One who knows how to observe men and things critically will find considerable differences. These dissimilarities are as old as Egypt itself. They have always existed, and are as much more intense as the communications between district and district were formerly more difficult. They are due to physical conditions special to each village, to the prevailing winds, the form and character of the mountains, the extent of cultivable lands, and the supply of water. A study of the detail of the country is a very important preliminary to the examination of Egyptian history. Every village and every nome had formerly its special divinity and its particular usages. Are we sure that the gods and customs were not imposed by local conditions? At Ombos two hostile gods were adored in the same temple. May we not see in this fact a recollection of the hostility which has always prevailed between the inhabitants of the two banks of the river, and still continues?

Previous, however, to investigating these details which have been so influential on Egyptian civilization, we ought to dispel the darkness which hides from us the earliest traces of man in the valley of the Nile, and examine how man lived in his beginning, to study the geology of the country and its condition when it issued from the seas. As one of the results of this study we find that palæolithic man, known to us only through the rough-cut flints we find in the alluvions, made his first appearance. After this period of excavation came that of filling up with silt, which still continues. New evidences of man appear in his burial places and the ruins of his villages, the kitchen middens which he has left in his habitations of unburned brick and in his camps. This time he is more civilized; he chips his flints with a skill that is not surpassed in European neolithic implements; he makes vessels of stone and clay, covers them with rude paintings, sculptures animal forms of schist, and wears necklaces of the shells and the stones of the country. Then comes a foreign people to take possession of Egypt, bringing knowledge of metals, writing, hieroglyphics, painting, sculpture, new industries and arts that have nothing in common with the arts of the people it has overcome. The ancient Pharaonic empire begins, or perhaps the reign of the divine dynasties. The men with stone implements are the aborigines; the others are the conquering civilized Egyptians. Nothing can be more interesting than a comparison of the arts of the aborigines and those of the Egyptians of the earlier dynasties. Nearly all their characteristics are different, and it is impossible to regard them as of common origin. Yet some of the native forms persisted till the last days of the empire of the Pharaohs. These aborigines belonged to a race that is now extinct, they having been absorbed into the mass of the Egyptians and Nubians among whom they lived, and from this mixture the fellah of ancient times is derived. The origin of the conquering race--of the Egyptians as we know them--has not been precisely determined. The weight of evidence, so far as it has been obtained, and the balance of opinion, are in favor of an Asiatic origin and of primary relationship with the Shemites of Chaldea.

In Egypt more than in any other country it is necessary to proceed with the most scrupulous circumspection in the examination of remote antiquities. The relics of thousands of years of human life have been piled one upon another and often intermixed. The questions they raise can not be answered in the cabinet or by the study of texts; but the inquiry must be prosecuted on the ground, by comparison of the deposits where they are found and in the deposits from which they are recovered.

From my first arrival in Egypt, in 1892, my attention has been greatly occupied with the question of the origin of the relics of the stone age that have been found from time to time in that country. I have gathered up the scattered documents, explored a large number of sites, and have bought such flint implements as I have found on sale. I have gradually been led to believe that while some of these cut stones may possibly belong to the historical epoch, we shall have to attribute a much more remote antiquity to the most of them, and that evidences of a neolithic age in the valley of the Nile are more abundant than has generally been supposed.

In many minds the historical antiquity of Egypt, the almost fabulous ages to which its civilization ascends, seem to challenge the history of other countries, and the land of the Pharaohs, rejecting all chronological comparison, to have appeared in the midst of the world as a single example of a land which savage life had never trodden. Yet what are the centuries since Menes ruled over the reclaimed valleys, the few thousand years of which we can calculate the duration, by the side of the incalculable lapse of time since man, struggling with the glaciers and the prehistoric beasts, began his conquest of the earth? The antiquity of Egypt, the eight thousand years (if it be as many) since the first Pharaoh, are only as an atom in the presence of these ages. We can assert some vague knowledge of these pre-Pharaonic inhabitants, for two hatchets of the Chellean pattern were found some time ago in the desert, one at Esnet, the other near the pyramids of Gizeh; and we can now affirm in the most positive manner that Quaternary man lived in the country which is now Egypt, and was then only preparing to be. Four palæolithic stations have been more recently discovered--at Thebes, Tukh, Abydos, and Daschur. Join these sites to the other two where isolated pieces were found, and we have the geography of what we know at present of Chellean man in the valley of the Nile. Doubtless continuous researches would result in similar discoveries at other points, for I have met these relics wherever I have been able to make a short sojourn. The Chellean implements are found in the gravels of the diluvium on the pebbly surface. They have been disturbed and probably scattered, but some places yield them more numerously than others--points possibly corresponding to the ancient workshops. I have found a considerable number of specimens at Deir-el-Medinet; M. Daressy, of the Bureau of Antiquities, found a perfectly characteristic Chellean hammer stone in the Yalley of the Queens at Gurneh, as perfectly worked as the best specimens found at Chelles, St. Acheul, and Moulin-Quignon.

The finds are not very numerous at Tukh, but one may in a few hours make a collection there of hatchets (or hammer stones), scrapers, points, simple blades, and a large number of stones bearing indisputable marks of having been worked, but not presenting precise forms. The deposit at Abydos is in the bottom of a circle behind the ruins surrounding the Pharaonic necropolis. The specimens seem sufficient to prove the existence of Quaternary man in Egypt, while the search for them has hardly yet begun. In view of them it is extremely improbable that man did not also exist there during the long period that intervened between this primitive age and that of the earliest Egyptians who had metals. He did exist there then, and the evidences of it are found in neolithic remains between Cairo and Thebes, a distance of about eight hundred kilometres along the valley of the Nile, in the Fayum, and in Upper Egypt. Among these are the remarkable tombs at Abydos which have been explored by M. E. Amélineau, and of which he has published descriptions. They belong to a category which I have characterized as tombs of transition and as signalizing the passage from the use of polished stone to that of metals. Their archaic character can not be disputed, and their royal origin is probably certain. They may belong to aboriginal kings or to the earliest dynasties. They reveal a knowledge of brass and of the use of gold for ornament. At the necropolis of El-'Amrah, a few miles south of Abydos, are some archaic tombs, all of the same model, composed of an oval trench from five to six and a half feet deep. The body is laid on the left side, and the legs are doubled up till the knees are even with the sternum; the forearms are drawn out in front and the hands placed one upon the other before the face, while the head is slightly bent forward. Around the skeleton are vases, and large, rudely made urns, often filled with ashes or the bones of animals, and nearer to them are painted or red vessels with black or brown edges, vessels roughly shaped out of stone, and figurines in schist representing fishes or quadrupeds, cut flints, alabaster clubs, and necklaces and bracelets of shells. Bronze is rare, and found always in shape of small implements. Both purely neolithic tombs and burials of the transition period to metals occur at El-'Amrah. The most remarkable feature of the burials is the position of the corpse, totally unlike anything that is found of the Pharaonic ages.

The Egyptian finds of stone implements present the peculiarity as compared with those of Europe, that types are found associated together belonging to what would be regarded in other countries as very different epochs. The time may come when subdivisions can be made of the Egyptian stone age, but the study has not yet been pursued far enough to make this practicable at present. Among these articles are hatchets showing the transitions, examples of which are wanting in Europe, from the rudest stone hammer to the polished neolithic implement; knives of various shape and some of handsome workmanship; scrapers, lance heads, arrowheads, saws, pins, bodkins, maces, beads, bracelets, and combs. The large number of instruments with toothed blades found at some of the stations may be regarded as pointing to a very extensive cultivation of cereals at the time they were in use. The deposits of Tukh, Zarraïdah, Khattarah, Abydos, etc., situated in regions suitable for growing grain, yield thousands of them, while they are very rare at the fishing station of Dimeh. That the use of sickles tipped with flint very probably lasted long after the introduction of metals seems to be proved by the hieroglyphics; but very few evidences of the existence of such tools are found after the middle empire.