Overcrowding

“ Frost, fire, insects, and floods, by destroying the trees or their seeds, may retard the progress of the species. The wind may be unfavorable. The seeds hang upon the trees ready and ripe for germination, but a breeze comes [Pg 85] along and carries them to a place where the conditions are ill adapted to their peculiar nature. The following year the wind is propitious and the little trees soon start into life. ”

“ But where growth is on a stupendous scale, there decay is exuberant, for “the powers that build are the powers that putrefy.” Above are light, warmth, and moisture: such are conditions of growth. Below are darkness, warmth, and moisture: such are conditions of decay. Which is more effectual, that mighty power of evolution elaborating “the rain-water hurrying aloft” into tissue of leaf and flower, or those great forces of dissolution which can so soon transmute the fallen trunk of iron-wood into a pregnant, humid mound? ”

“ If those proper to winter were observed, all plants and trees would wither early, and afterwards there would be great floods, destroying city and suburban walls. If those proper to spring were observed, there would be the calamity of locusts, violent winds would come, and plants in flower would not go on to seed. ”

“ The curtailment of the trunk, by its immersion in the river, quite destroys the fair proportions of the tree, and thus makes us sensible of a regularity and propriety in the usual forms of nature. The flood of the present season-- though it never amounts to a freshet on our quiet stream--has encroached farther upon the land than any previous one for at least a score of years. ”

“ These waters accumulate, and, overflowing the banks, spread out over the lowlands, resulting in the formation of a well-defined flood plain. This is a periodical occurrence with mature streams, and it occurs more or less regularly with all that are not torrent-like in character. The effect of the overflow is to destroy or to place at a disadvantage those plants of the flood plain that are not hydrophytes. At the same time, a thin layer of fresh silt is deposited upon the valley floor of sand or alluvium. Flooding is most frequent and of longest duration near the banks of the stream. ”

“ When a season favourable to it, or a diminution of creatures detrimental to it, causes any species to become more numerous than usual, an immediate increase of certain destructive influences takes place. If it be a plant, the supposed greater abundance itself implies fuller occupation of the places available for growth—an occupation which, leaving fewer such places as the multiplication goes on, becomes a check on further multiplication—itself causes a greater mortality of seeds that fail to root themselves. ”

“ We do not know whether this is an awkward effort towards increase—that these branches, under the influence of a not entirely matured instinct or faculty, droop in search of earth to root, and extend by layers, in conformity to a habit of some tribes of trees, in which this mode of increase is efficient, or that it is a disease unconnected with design or final cause. ”

“ By degrees its bed begins to sink, and the glassy smoothness is disturbed by a slight ripple. The inverted trees, that before lay so softly still upon its bosom, become twisted and tortured till they lose their form, and seem madly to mix in the tumult that destroys them. The current becomes more rapid at every step, till rock after rock has chafed the stream to fury, making the green one white. This lasts for a mile, and then down sink the rocks at once, one hundred and fifty feet, and the enormous flood falls after them. God said, let there be a cataract, and it was so. ”

“ Overflow in the spring season before growth has begun, or when it is about starting, will be helpful rather than harmful, especially if some deposit is left on the land by the subsiding waters. But if the overflow should be deep and of any considerable duration, and, moreover, if it should occur when the clover was somewhat advanced in growth, and in hot weather, the submergence of the clover would probably be fatal to it. ”

“ Cyclo., "a failure of the ordinary vital powers to carry on the healthy processes of life seem ordinarily to be the inviting cause of such a development of these plants as would constitute a disease," but we conceive that it is only after life is destroyed and decomposition set in that the Sphæria commences to germinate,—our friends however must observe and judge for themselves. ”

“ Raindrops, born a long way up in the hills, united to run through fissures in the earth, through soil-drains, through runnels in the moss of woods, through channels in the clay of sodden fields, each drop bearing infinitesimal grains of what, towards the sea at the end, becomes alluvial soil—each drop quarried, each drop carried, each drop endured for its moment, and then went hence and was no more seen. ”

“ These examples show us that the kind of change suggested above is actually going on, and has presumably always been going on in nature throughout the long geological epochs during which the development of flowers has been progressing. The two great modes of gaining increased vigour and fertility—intercrossing and dispersal over wider areas—have been resorted to again and again, under the pressure of a constant struggle for existence and the need for adaptation to ever-changing conditions. ”

“ There the overflow is astonishing, for no sooner has the 439 water reached the upper part of the banks than it rushes out and overspreads the whole of the neighboring swamps, presenting an ocean overgrown with stupendous forest-trees. So sudden is the calamity that every individual, whether man or beast, has to exert his utmost ingenuity to enable him to escape from the dreaded element. ”

“ Where the plant is sinking from mere old age, a source of decay of which in some kinds at least we have doubts, or from the soil being improper or exhausted for the particular kind of plant by long occupancy, or from any circumstance not admitting of remedy, the attempt to heal up the wounds caused by cutting out the diseased parts, or to induce new vigour by cropping the top, must be abortive, or only attended with partial or temporary success. ”

“ Every rootlet lends itself to steady the growing giant, as if in anticipation of fierce conflict with the elements. Sometimes its upward growth seems checked for years, but all the while it has been expending its energy in pushing a root across a large rock to gain a firmer anchorage. Then it shoots proudly aloft again, prepared to defy the hurricane. The gales which sport so rudely with its wide branches find more than their match, and only serve still further to toughen every minutest fibre from pith to bark.
The acorn planted in the deep forest shoots up a weak, slender sapling. ”

“ The cause of sinking in all cases lay in the decay of the outer fleshy covering. As I have observed in river and sea drift, fish bite at the floating fruits, and in this manner the seeds would soon be liberated and sink. The seeds of all the plants sank at once in my experiments except with one species, where the seed loosely filled its test and thus a floating-power of a few days was acquired. ”

“ Anomalous successions are those in which the physical change in the habitat is relatively slight, resulting in a displacement of the ultimate stage, or the disturbance of the usual sequence, merely, instead of the destruction and reconstruction of a formation, or the gradual development of a new series of stages on new soil. In nature, the ultimate grass or forest stage of a normal succession is often replaced by a similar formation, especially if the facies be few or single. ”

“ A stable formation, such as a forest or meadow, which acts as a decided barrier to invasion from adjacent vegetation, may disappear completely, as a result of a landslide, flood, or burn, or through the activity of man, and may leave an area into which invaders crowd from every point. Often, without undergoing marked change, a formation which has presented conditions unfavorable to the ecesis of species of mesophytic character may, by reason of a temporary change in climate, become sufficiently modified to permit the invasion of mesophytes. ”

“ When a recently felled tree is exposed to the action of water, or when bushes or grass and weeds are killed by being flooded, the sap and more soluble matters are leached out and putrefy or undergo other forms of decomposition. If the matter is alternately flooded and left bare, decay takes place fast. ”

“ Winter storms shattered the deserted sheds; props gave way and allowed great masses of earth to fall on the discarded stone; earth and moss, living green cushions, filled in the unsightly tool wounds. ”

“ Another dangerous obstruction is a tree becoming undermined and falling into the river, and the roots fastening themselves in the muddy bottom, while, by the constant action of the current, the limbs wear off, and the body keeps sawing up and down with great force, rising frequently several feet above the water, and then sinking as much below. ”

“ Coming down in flood from the moors the Exe will not wait to run round its curves, but rushes across the intervening corner, and leaves behind, as it subsides, a mass of stones, fiat as slates or scales, destroying the grass. ”

“ It is simply a smothering of the lower branches by those next above them, which has destroyed their vitality, and their decay has soon followed; while a new growth of branches at a higher point, in turn, performs the same office of destruction upon those next below them. As there is no outlet for the wood-growth but in an upward direction, upwards they must needs go, and as there is no light nor air for lateral branches under such a canopy of shade, death and decay ensue, and down they perforce must come. ”

“ Slowly we manage some little, patient self-improvement; gradually, inch by inch and bit by bit, we may be growing better, and then there comes some gust and outburst of temptation; and the whole painfully reclaimed soil gets covered up by an avalanche of mud and stones, that we have to remove slowly, barrow-load by barrow-load. ”

“ Conditions under which rapid dispersal has obviously an advantage occur when by some exceptional circumstances the natural vegetation is destroyed within an area, as by a flood or landslide. Such conditions are produced artificially each season over much of our own country by the operations of agriculture. ”

“ The destruction which began by the convulsions of nature is being completed by her slower processes. Trees are growing inside the buildings, and smaller plants find foothold in every crack and cranny, whilst into the surfaces of the rubble and adobe walls innumerable bees bore holes in which to deposit their eggs and thus prepare the way for further destruction from the heavy rains. ”

“ If you cut off a branch of a plant it stops growing, because the sap does not come to it any longer. It soon dies and decays. So, if the arm of a child be cut off, it can not grow, because no [2008] more blood can come to it. Like the cut-off branch, it dies and decays. ”

“ In the great circling whirlpools formed by the opposing forces, the bloated carcases of drowned animals, great branches of trees, or whole trees with a tangled mass of roots, swept round, lashed by the rain and whirling flood into semblance of some living monster, stretching octopus-like arms. ”

“ In the origin of normal successions, nudation may be brought about by the production of new soils or habitats, or by the destruction of the formation which already occupies a habitat. In a few cases, the way in which the habitat arises or becomes denuded is not decisive as to the vegetation that is developed upon it, but as a rule the cause of nudation plays as important a part in the development of a succession as does the reaction exerted by the invaders. ”

“ Flora and all her progeny have been utterly banished from its inhospitable soil, but it bids defiance to the flood: for thousands of years the elements have wreaked their fury on its mass; lightnings have burst upon its summit ”

“ As a balloon collapses if you prick it with a pin, and let out the air, so the cell walls collapse when the cells lose their water; and when the cell walls of a leaf collapse, the leaf itself collapses. ”

“ Then a change comes over its dream; there is a terrible and steady downpour; ere twenty-four hours have elapsed, the new blades of grass can be seen peeping out; there are innumerable insects on the wing, and millions of frogs are croaking in the marshes. ”

“ But besides the stones and gravel and mud carried down by a river, we must also consider the fate of the remains of plants and animals that are swept along by it, -56- especially in flood-time. In any ordinary flood trees and shrubs, and the smaller animals like mice and moles and rabbits, are drowned by the flood. In greater floods birds and even large animals are drowned, and their remains are buried in the sediment. If they are quite covered over they may perhaps be preserved, and their bones may last for an indefinite period. ”

“ Now, as this shelly integument envelops them from their earliest youth, and as it does not expand and grow, the natural growth of the soft body beneath would be entirely prevented did not nature supply a remedy of a very curious kind—the exuviation, or periodical throwing off of the external crust, and the formation of a larger shell-covering fitted for the increasing growth of the animal. ”

“ Indeed, it seems wonderful that the unfortunate people ever reaped any harvests at all, when we read the list of forces arrayed against them. If there were no inundations, sweeping away the produce of their fields, to say nothing of the houses in which they lived and occasionally the men themselves, there was pretty sure to be a drought; or if not a drought, a swarm of grasshoppers or of locusts would devastate the plains, selecting, as, with a sort of infernal instinct, such creatures do, the richest and most fertile districts as their prey. ”