Part 6 (1/2)

Among the leading propositions laid down by Arthur Renfrey, Esq., F.R.S.

etc., etc., in the able article prepared by him for ”The Physical Atlas of Natural Phenomena,” by Alexander Keith Johnston, Edinburg Edition, 1856, on ”The Geographical Distribution of the most Important Plants Yielding Food,” are the following:--

1. ”The primary condition of the existence of any species of plant, is its absolute creation, of which we know nothing.

2. ”But we a.s.sume each species to have been _created but once in time and in place_, and that its present diffusion is the result of its own law of reproduction under the favorable or restrictive influences of laws external to it.[14]

3. ”The most important of external laws are those relating to climate, since _any species can flourish only within narrower or wider, but always fixed limits, of temperature, humidity etc_.,

4. ”The climate depends primarily on lat.i.tude, since this indicates distance from the source of heat, and the degree of obliquity of the heating rays.”

There are other governing conditions, of course, such as the average rain-fall, distance from the equator, the elevation above the sea level in the various mountain systems of vegetation, etc., including the hygrometric, thermometric, telluric, and other conditions, of the several localities in which the different species of vegetation make their appearance.

But why should this distinguished naturalist insist upon the specific creation of either plants or animals? No scientific work of any paramount value confines the creative power of the universe to such narrow and restricted limits. Nor is there a particle of evidence to be drawn from the Bible that either plants or animals primarily originated in pairs.

”Let the earth bring forth” is a command without limitation, or restriction, as to time, place, or number; and there is no reason to doubt that myriads of living forms swarmed everywhere, at first as now, in nature.

The idea, as expressed by Mr. Renfrey, that they were specifically created at one time and place only, whether in pairs, tens, twenties, or hundreds, is neither a rational one, nor has it any experience-argument or scientific authority on which to stand. Take, for instance, an experience-argument directly in point:--When the salt wells were first bored at Syracuse, N.Y., and the salt water was suffered to flow in waste over the low grounds about the salt-works, the small saline plants peculiar to salt-marshes in the warm temperate zone made their appearance, not in pairs, tens or hundreds, but in thousands rather, and have nourished there ever since. They came because conditions favored; because a salt-marsh had been artificially produced hundreds of miles away from the sea coast. This is only one of a large number of cases--more than we have room to specify in this connection--showing that wherever man, artificially or otherwise, produces the necessary conditions of plant-life, nature responds to the germinal law precisely as she did millions of years ago when the first salt-marsh favored the appearance of these saline plants--such as grow under no other conditions or circ.u.mstances.

But this idea of plants coming primarily from a single pair of progenitors, and each primordial pair branching off into diversified offspring, as in the case of the cabbage, a.s.sumed to be the original ancestor of all the turnips and ruta-bagas, may be an article of botanical faith, but never of experimental proof. ”_Entia non sunt multiplicanda prA

ter necessitatem_” is an old and well-approved maxim, applicable alike to the countless myriads of living organisms, as to the innumerable crystalline forms to be found everywhere in nature. Nothing is produced without the necessary conditions on which its production depends.

”Necessity,” in its primitive signification, is a term of the very widest meaning, and most universal application. It applies as well to the course of nature as to the course of human events--to the laws of vegetable and animal growth as to the inevitable march and order of celestial movements.

As applied to any form of life-manifestation it implies a law of development and growth, as well as the physiological conditions without which vital manifestations are impossible. For law, in a physiological sense, is that mode of vital action by which effects are invariably and inevitably produced.[15] And this law is just as dependent on necessary vital conditions as vital manifestations are dependent on a physiological law. There must always be this reciprocal dependence and relations.h.i.+p between conditioning causes and effects. Whenever and wherever the necessary vital conditions exist, the physiological law takes effect, and the requisite vital manifestation is witnessed. And this is no doubt as true of animal as of vegetable life.

The earth's surface has been divided into eight separate zones, each of which is distinguished by its peculiar or characteristic fauna and flora.

Their order, measured from the geographical equator, is as follows;

1. The Equatorial Zone, extending from 0A deg. to 15A deg..

2. ” Tropical ” ” ” 15A deg. ” 23A deg..

3. ” Sub-tropical ” ” ” 23A deg. ” 34A deg..

4. ” Warm Temperate ” ” ” 34A deg. ” 45A deg..

5. ” Cold ” ” ” 45A deg. ” 58A deg..

6. ” Sub-arctic ” ” ” 58A deg. ” 66A deg..

7. ” Arctic ” ” ” 66A deg. ” 72A deg..

8. ” Polar ” ” ” 72A deg. ” 82A deg..

These several zones become sixteen in number when considered with reference to both the northern and southern hemispheres. And a like division of isothermals is made in the case of all our mountain systems, extending in both directions from the equator. In ascending our equatorial, tropical, and sub-tropical mountains, we find, of course, at their several bases, the temperature of the zones in which they respectively lie; from two thousand to three thousand feet, we reach the next higher zone, and so on, at about the same ratio of alt.i.tude, until we ascend to the polar zone or the line of perpetual ice and snow. The peak of Teneriffe, for instance, lies in the sub-tropical zone, but, at the elevation named, we meet with the vegetation which characterizes the warm temperate zone. And this holds true of all our mountain systems, in all lat.i.tudes, and at all alt.i.tudes, in all parts of the globe.

They all present the same or strikingly similar characteristics in plant life, with such variations and modifications only as might be accounted for, were all the influencing conditions and surrounding circ.u.mstances, modifying geographical distribution, known to us. From the lowest to the highest regions in which vegetation flourishes, this rule, with slight exceptions only, will be found to obtain, and it is in this direction that the observations of the scientific, as well as practical botanist, should hereafter be extended.

Humboldt noticed this characteristic feature of the earth's vegetation quite early in his explorations, and accordingly divided the tropical mountains, as the earth's surface was then divided, into three separate zones, the tropical, the temperate, and the frigid. But a closer cla.s.sification now distinguishes them into the same number of zones as are marked, in approximate isotherms, on the earth's surface. Mr. Renfrey gives us further statistics of great value respecting these several plant zones of the globe, all of which fit so admirably into our theory of plant-distribution, that we can hardly see how the most prejudiced mind can resist the force of its application. Among the most important of these statistical facts are tables giving the comparative rain-falls in the different plant zones of the old and new worlds, and the cla.s.ses of vegetation peculiar to each of them.

The Equatorial zone, for instance, is characterized by extreme luxuriance in growth, owing no doubt to the great heat and abundant moisture therein, and exhibits a vegetation which is peculiar to itself, and which could only thrive under the hygrometric, thermometric, telluric, and other conditions of that extensive zone.

The Tropical zones (those north and south of the equator) are characterized by a more abundant and diversified underwood, and, while retaining some of the equatorial forms, present fewer parasites and less rapid and luxuriant growths. They contain many plants and trees which are peculiar to their own limits, and these are generally the hardiest and most abundant. All equatorial forms disappear in these zones, that is do not pa.s.s into the sub-tropical zones. And these characteristics obtain in both the northern and southern tropical zones, as well as in the mountain systems within the equatorial regions.

The Sub-tropical zones, while retaining some of the more marked forms and general features of the tropical zones, such as palms, bananas, etc., exhibit the most striking characteristics of their own, consisting of a greater abundance of forest trees, especially those having broad, leathery and s.h.i.+ning leaves, like the magnolias, the different species of laurels, and plants of the myrtle family. The tropical forms all disappear in these zones, as the equatorial do in the tropical zones.

The Warm Temperate zones exhibit the same disposition to retain some of the hardier and more abundant sub-tropical forms that characterize the other zones, in respect to their adjoining isotherms. But the trees and plants peculiar to this zone north, (and the same is no doubt true of the corresponding zone south), are more numerous, and embrace a wider range of deciduous, as well as evergreen growths. Evergreen shrubs, heaths, cistusses, and leguminous plants are everywhere more abundant. The marked characteristic of these zones is that the trees, plants, and arborescent gra.s.ses differ more widely in their general character, as well as run more extensively into varieties.

The Cold Temperate zones retain many of the deciduous trees of the warm temperate, but with less conspicuous blossoms, while a stronger tendency is shown toward social conifers, and the trunks of the deciduous trees are more profusely overrun with mosses, lichens, etc. These zones are also abundant in gra.s.ses.