CHAPTER XXV.

RECOGNITION OF THE CHARACTER OF SOILS FROM THEIR NATIVE VEGETATION. UNITED STATES AT LARGE. EUROPE.

The application of the above data outside of Mississippi can mostly be verified only in a fragmentary way from such data as are casually given in the reports of State Surveys, as well as from such observations as the writer has been able to make personally elsewhere. In the latter category the most copious refer to the states of Alabama, Louisiana and Illinois.

ALABAMA.—The observations of Prof. Eugene A. Smith, and those of Dr. Chas. Mohr, are especially valuable and cogent as to the close correspondence of the soil and vegetative phenomena with those observed in Mississippi. They are faithfully reproduced on the corresponding geological areas, including also the Flatwoods. Northwest of Mobile, on the Mississippi line, the long-leaf-pine forest is interspersed with more or less continuous areas bearing a fine oak growth, with hickories and other trees indicating a calcareous soil. This feature is most extensively developed in Alabama in what is known as the “lime-sink region,” on the borders of which the vegetative transition in passing from the non-calcareous sandy pine land, can be observed in the most striking manner and with frequent alternations. Northward of the long-leaf-pine belt, the tertiary and cretaceous areas show in Alabama the same features as in Mississippi, viz., black calcareous prairies alternating with ridge lands, among which in the cretaceous area the Pontotoc ridge is represented by a series of isolated knobs, popularly known as Chunnenugga ridge, closely resembling the former in its soils and vegetative character.

See Plant Life of Alabama, by Charles Mohr, Vol. VI. Contr. U. S. Nat. Herb., U. S. Dep’t Agr.; Alabama Ed. of Same, Ala. Geol. Survey, 1901.

In northern Alabama, according to Dr. Smith, on the various stages of the Carboniferous formation, ranging from a sandy or conglomerate character to that of limestones of various degrees of purity, soils contrast strikingly with each other, agreeing closely with those seen in the neighboring part of Mississippi. Here, moreover, the contrast between the natural vegetative character as well as cultural value of the lands derived from the magnesian limestones (the “barrens”) contrasts strikingly with those originating in the purer limestones, on which the blue grass is at home.

LOUISIANA.—As to Louisiana, whose geological formations correspond closely to those of Mississippi, it may be said in general that the vegetative phenomena coincide completely with those observed in Mississippi. The “white-lime country” of northeastern Mississippi is represented in Louisiana only by patches occurring here and there on a line laid from Lake Bistineau to the coast at Petite Anse Island. But the chief characteristics of the calcareous area, among them especially that of the occurrence of red cedar and clumps of crab-apple, persistently reappear. The “Central Prairie Region” of Louisiana is quite narrow, but on it there reappear precisely the same characteristics described in connection with that area in Mississippi. In the long-leaf-pine region of Louisiana there occur, as in Mississippi, some isolated patches of a calcareous character, the largest of which is on the Bayou Anacoco in Vernon Parish, near the western border of the State. As we emerge from the sandy lands of the long-leaf pine area to that underlaid by the calcareous formation, we find, first, a change to oak and short-leaved pine, then the oak forest alone; finally, on a level black prairie of considerable extent, the post and black-jack oak in their thick-set form, clumps of crab-apple, red haw and honey locust, here and there a red cedar; exactly as has already been described in connection with the prairie lands of Mississippi. To southward of the long-leaf-pine area lies a broad belt of level, generally treeless, sandy prairie, in part dotted with groves of timber, but otherwise with nearly the same peculiar, small-seeded herbaceous vegetation observed in the corresponding portion of Mississippi. But in Louisiana there intervenes between these gray sour lands and the shell hammocks of the immediate sea-coast with their groves of live-oak, a belt of black calcareous prairie, increasing in width and clayeyness towards the West, and acquiring considerable extension in the corresponding portion of Texas. On these prairies we again find the calciphile vegetation, including the honey locust, clumps of crab-apple and red haw, etc., but not usually any oak growth, except (near the sea-coast) the live-oak. In the hilly country of northern Louisiana there is reproduced substantially the vegetative character of the “short-leaf pine and oak” uplands of Mississippi (see map on p. 490, chapter 24), save in that, owing to the occasional outcropping of the calcareous materials of the Tertiary, small prairies with black soil are spotted about here and there. Bordering the Mississippi Bottom there are a series of oak-upland ridges with a brown loam soil corresponding to the fertile area in northwestern Mississippi, with small patches of the “Cane hills” loess soils, bearing a corresponding tree growth.

See “Final Report of a Geological Reconnoisssance of Louisiana,” published by the New Orleans Academy of Science in 1871.

In Western Tennessee the vegetative zones so distinctly shown in the adjacent portion of Mississippi are not so strikingly outlined, but so far as they do exist, the phenomena observed accord exactly with those heretofore described. The same holds true of Western Kentucky, as is well set forth and graphically described in the reports of the geological surveys of that state by Dr. David Dale Owen, and later by Dr. R. H. Loughridge.

North Central States.—North of the Ohio River the materials of the geological formations are not nearly as much varied as they are south of the same; consequently the vegetative features are also much more uniform. It must be remembered that from the Alleghenies nearly to the Mississippi, the states of Ohio, Southern Michigan, Indiana and Illinois are largely covered by drift deposits overlying the older formations, except that along the Ohio and Mississippi rivers lies the calcareous loam of the Loess or Bluff formation.

Within the states mentioned, however, not only are the older underlying formations very generally calcareous, but calcareous sand and gravel form a large proportion of the drift deposits, which in most cases overlie the rocks. Hence we find from the Alleghenies to the Mississippi a predominance of the oak forests which characterizes calcareous soils, as in the better class of uplands in Mississippi and Tennessee; interrupted only here and there by sandy belts or ridges bearing inferior growth, among which, again, the black-jack and post oaks, with short-leaved pine, are conspicuous. But in a large portion of Illinois, as well as in Western Indiana, the oak forest is interrupted by more or less continuous belts, and sometimes by a wide expanse, of black prairie, generally treeless or bearing only clumps of crab-apple and haw, and underlaid more or less directly by the carboniferous limestones, whose disintegration has materially contributed to the black prairie soils; which are noted for their high and long-continued productiveness. The lower ground is characterized, besides clumps of crab-apple and red haw, by the frequent occurrence of the honey locust, the lead plant (Amorpha fruticosa), the button-bush (Cephalanthus occidentalis), and among herbs by the polar plant (Silphium laciniatum), the prairie burdock (S. terebinthinaceum), the swamp rose-mallow (Hibiscus moscheutos), the sneezewort (Helenium autumnale), the wild indigo (Baptisia tinctoria and leucophcæa).

The black-jack and post oak are not nearly as frequently found on the prairies of Illinois as on those of Mississippi and Alabama; but where they occur they assume a similar habit, including the occurrence of the dwarfed, apple-tree-shaped form on the low ridges with heavy yellow clay soil, that sometimes intersect the prairies. The post oak, moreover, in a form quite similar to that described as occurring on the Flatwoods of Mississippi, forms the timber of the “post oak flats” occasionally found between the low ridges bordering the streams, or along the edges of the prairies. The herbaceous vegetation of these post oak flats distinctly characterizes them as being poor in lime. In the loamy uplands, where the calcareous ingredient is more abundant, the open-headed form of the black-jack and post oak are also found, interspersed with a luxuriant growth of black, red and white oak, with more or less of hickory, which here assume a magnificent development, much superior to that seen south of the Ohio. These yellow-loam uplands correspond very closely in their soil-composition and agricultural character to the brown-loam area of Mississippi and Tennessee, which lies inland from the Loess belt. Where these uplands approach the prairie or the outcrops of a limestone formation, there is usually added to the oak growth the linden, the wild cherry and the ash; the latter two also usually appear in the bottoms of the streams and on the slopes adjacent, together with the walnut and butternut, and in the lowest ground the sycamore.

The tree growth of the Loess belt bordering the Ohio and Mississippi, so far as climatic differences permit, agrees almost precisely with that described in the corresponding portions of Mississippi and Tennessee. The change from the oak and hickory growth covering the yellow-loam uplands toward the more calcareous area is evidenced by the appearance of large sturdy trees of sassafras, together with the linden and sugar maple. Descending from the “bluff” toward the rich bottom-prairie with its black, heavy soil, we at once encounter the familiar indices of the more highly calcareous land, viz., the honey locust, clumps of crab-apple and red haw, with hackberry, Kentucky coffee tree and mulberry on the lower ground. In late summer and during autumn, a tall growth of the iron weed (Vernonia), several Eupatoriums (E. perfoliatum and purpureum, the white and the purple boneset) and of the blue-spiked Verbena are very characteristic, as are also several species of Cassia (Carolina coffee, etc.,) and the swamp rose-mallow.

Upland and Lowland Vegetation in the Arid and Humid Regions.—In the humid countries there is commonly a marked difference between the vegetation of the uplands and lowlands, arising not merely from the difference in the moisture supply, but evidently of a specific nature. When we discuss the characteristic plants in detail, it becomes obvious that it is lime vegetation that, in most cases, forms the characteristic differences between upland and lowland forest growth; a natural consequence of the leaching-down of the lime from the higher land to the lower levels. By way of counter-proof we find that when the uplands themselves are of a calcareous nature, a part at least of the lowland flora ascends into them. As prominent examples may be mentioned the Tulip tree (Liriodendron), black walnut, ash, Kentucky coffee tree, Hercules’ club, etc., which are lowland trees over the greater part of their area of occurrence; but in the loess or Cane hills bordering the Mississippi and its larger tributaries, as well as in the limestone regions of the southwestern and western states, are conspicuous in the uplands as well. The tall southern cane (Arundinaria macrosperma), usually considered a plant of the low river bottoms, originally covered the loess or “Cane hills” of the lower Mississippi, with their highly calcareous soils. The same is true of many other trees and shrubs characterizing limy lands. Of course there are some whose habitat is dependent upon the concurrent presence of both lime and moisture, such as the sycamore, cottonwood, hackberry, pawpaw, etc., which are naturally found only in stream bottoms or on low hammocks.

In the arid region, on the contrary, the main difference in upland and lowland vegetation is (outside of mountain influences) entirely referable to moisture-conditions; the proof being that so soon as the uplands are irrigated the lowland flora takes possession. Both uplands and lowlands being abundantly calcareous, there then is no cause for any material differences. This substantial uniformity of upland and lowland plant growth is particularly striking in the comparatively restricted floras of Eastern Oregon and Washington, and in Montana, where the more luxuriant growth of the valleys is almost the only contrast seen when their vegetation is compared with that of the uplands adjacent.

Forms of Deciduous Trees in the Arid Regions.—Since, as shown above, the soils of the arid regions are almost throughout calcareous, we should expect that the forms of the native trees would in general conform to the rule given above. As regards the deciduous trees this is very generally true: We rarely see on the Pacific slope, south of Oregon, anything to compare with the tall oaks of the Atlantic forests. The native oaks are as a rule of low, spreading growth, with stout, short trunks; and as they rarely form dense forests, the timbered areas have an orchard-like appearance, characteristic of the landscapes of the arid region, from the Mezquit Plains of Texas to Eastern Oregon and Washington. Only where a very abundant supply of moisture prevails do we find occasional exceptions. The trees of the humid region when transplanted to California have a perverse tendency to branch low, so that only the most persistent trimming-up will induce them to form trunks at all like those found in their native climes. In some cases no amount of trimming will result in the formation of anything more than bushes.

It may be objected that the arid climate as such, and not the calcareous nature of the soil, is the cause of this tendency. It is unquestionable that this low-branching habit is a distinct advantage to the plants, whose trunks would otherwise be frequently scorched by the hot summer sun; as happens when Eastern settlers try to grow “standard” fruit trees, with the result that a “sore,” or sunburnt streak is formed on the southwest side of the exposed trunk. All orchard trees should therefore be pruned “vase-shape” in arid climates, partly for this, partly for other reasons. But this cannot explain the fact that seedlings from eastern acorns act precisely as do acclimated trees; so that it is not a case of the survival of the fittest to endure arid conditions.

Tall Growths of Conifers. Moreover, while the rule holds good with almost all deciduous trees, it is not applicable to the Conifers; which in the case of the Sequoias (redwoods and “big-trees”), sugar pine and others, exemplify some of the tallest growths known in the world. The Eastern Cedar or Juniper grows tall only on sufficiently calcareous soils, and in the Mississippi Valley states at least, wherever it occurs is an unfailing indication of calcareous lands. The extended occurrence of the spruce on the Allegheny Ranges, where limestone formations prevail so largely, seems to indicate a similar preference for calcareous lands. And this is certainly true of the black locust, which reaches its extreme southern range in the cretaceous hills of Northeastern Mississippi, showing the stout, stocky form it also assumes when planted in the calcareous black-prairie lands of Illinois.

Herbaceous Plants as Soil Indicators. While herbaceous plants are not as generally considered by land-seekers in judging of soil fertility and character, it goes without saying that very many are quite as characteristic as the tree vegetation, especially when deep-rooting, so as not to indicate merely the character of a few inches of surface soil.

In the Middle West of the United States especially, a large number of the Compositæ serve as marks of high productive capacity. This is particularly true of the larger species of the sunflower tribe, among which Helianthus grosse-serratus and doronicoides are perhaps the most generally notable; while farther west, beginning with Kansas, the “Sunflower State,” and its northern neighbor, H. annuus, whether native or introduced, becomes conspicuous also. The Silphiums (compass sunflowers) have nearly the same significance, S. laciniatum and perfoliatum being prominent on the prairies of Illinois and Indiana; but in land under cultivation they are mostly replaced by a luxuriant growth of the Ragweed, Ambrosia trifida. Various species of Bidens (beggar ticks), notably the B. aristata and cernua, accompany the true sunflowers in the lower grounds of these regions, as do also Heliopsis laevis, Coreopsis triperis and Rudbeckia (Obeliscaria) pinnata. Rudbeckia hirta and purpurea, though also occurring on rich soils, are not characteristic of them. The larger species of golden rods (Solidago), notably S. canadensis, rigida and speciosa (not ordinarily distinguished by farmers) share substantially the distribution of the large sunflowers mentioned above. Of the Asters, only A. novæ-angliæ serves as a reliable guide to high-class lands in the Middle West, but a very copious growth of asters and solidago of various species is always a welcome indication of land quality, and indicates soils of good lime content, if not absolutely calcareous.

In view of its specific designation and the reputed poverty of New England soils, this is rather unexpected.

Leguminous Plants.—It is generally understood that most leguminous plants, and among them especially the clovers, indicate rich, or rather, calcareous lands. The very large proportion of lime contained in the ash of legumes at once creates this presumption, which is fully confirmed by experience so far as our ordinary culture plants of that relationship are concerned. The favoring effect of lime on the development of bacteria, so essential to the full development of cultivated legumes, has already been referred to. The favoring effect of gypsum sown even in small amounts with clover and other legumes, may probably be referable to the known action of that salt in promoting nitrification, which in the first stages of leguminous growth is so highly favorable to a vigorous and early start of the crop, and to a more copious production of the nitrogen-assimilating nodules. The quick change noted in meadows and pastures of languishing production so soon as moderately limed, by the appearance of clover among the herbage, at once reminds us that the Rhizobia do not flourish in acid lands. The great prevalence of leguminous plants of all kinds in the arid region—clovers (not fewer than twenty-three species in California alone), Lupins, Astragalus and related genera, at once remind us of the universal prevalence of calcareous soils in these regions, as shown above. Mutatis mutandis, we find precisely the same general facts in the arid regions of the other continents.

Nevertheless, it must be kept in mind that not all plants of the leguminous order are positively “calciphile.” Within the United States, it is especially the genera Desmodium (Meibomia) and Lespedeza, which are very numerously represented in the long-leaf pine region of Mississippi, where the soils are so poor in lime. Whether under these conditions these plants develop the rhizobian nodules, has not, so far as the writer is aware, been definitely observed. Certain it is that quite a number of these plants occur on both calcareous and non-calcareous soils, and on the latter assume a much more vigorous development than in the pine woods. But it is evident that they, with a few others (e. g. Galactia mollis, Cassia chamæcrista and nictitans) are more or less indifferent to the lime-content of soils, and cannot therefore be relied upon in judging the quality of lands. In Mississippi and northern Alabama, the Tephrosia virginica (“devil’s shoestring”), associated with chestnut and short-leaved pine, is characteristic of the poorest non-calcareous lands, and bears seeds but very scantily. It disappears so soon as calcareous lands are approached, together with the chestnut tree.

EUROPEAN OBSERVATIONS AND VIEWS ON PLANT DISTRIBUTION AND ITS CONTROLLING CAUSES.

The writer has thus far presented and discussed mainly his own observations made in the United States, without reference to the previous and contemporaneous work on the same subject in Europe. There arose certain discrepancies which could not well be explained without a previous full consideration of American conditions.

As is well known, for nearly twenty years the accepted theory in Europe was that of Thurman, which attributes the distribution of the native floras entirely to physical conditions; thus anticipating by more than half a century the corresponding hypothesis lately brought forward by the U. S. Bureau of Soils. Thurmann classes plants simply as hydrophile and xerophile, thus differing from most of our modern ecologists merely in omitting the transition phase of “mesophytes,” which now serves as a convenient pigeon-hole for an indefinite variety of plants.

Essai de Phytostatique appliquée à la chaine du Jura et aux contrées voisines. 2 vols. 8vo. Berne, 1849.

While gradually many were led by their observations to doubt the correctness of Thurmann’s exclusive physical theory, Fliche and Grandeau were apparently the first to impair by their investigations the confidence in the accepted view. They investigated exhaustively the conditions under which the maritime pine and the chestnut tree, both antagonistic to lime, would flourish, and proved that the presence of any considerable amount of lime in the land would cause them to languish or die, although the physical conditions so far as ascertainable were exactly alike. It is interesting to note what were the lime-percentages which caused these differences; viz., for the “non-calcareous” soil and subsoil, respectively, .35 and .20%; for the calcareous land, 3.25 and 24.04%, the latter evidently being decidedly “marly.” The composition of the ash of these trees is very instructive, and is therefore given in full. Alongside of the ash of the maritime pine on the two soils is given that of the Corsican pine, a lime-loving tree.

COMPOSITION OF PINE ASHES ON CALCAREOUS AND NON-CALCAREOUS LANDS. -----------------+-------------------------------+-------------- | MARITIME PINE, | CORSICAN PINE, | PINUS PINASTER. |PINUS LARICIO. -----------------+-----------------+-------------+-------------- |On non-calcareous|On calcareous|On calcareous | soil. | soil. | soil. | | | Potash | 16.04 | 4.95 | 13.56 Soda | 1.91 | 2.52 | 2.24 Lime | 40.20 | 56.15 | 49.13 Magnesia | 20.09 | 18.80 | 13.49 Ferric Oxid | 3.83 | 2.07 | 3.29 Silica | 9.18 | 6.42 | 7.14 Phosphoric acid | 9.00 | 9.14 | 11.33 -----------------+-----------------+-------------+-------------- Total | 100.25 | 100.04 | 100.18 -----------------+-----------------+-------------+-------------- Ash per cent. | 1.32 | 1.54 | 2.45 -----------------+-----------------+-------------+--------------

Annales de Chimie et de Physique, 4me série, tome 29; ibid. 5me série, Tome 2. Also, ibid, tome 18, 1879.

It is very interesting to note in these analyses the inverse ratio in the absorption of potash and lime by the maritime pine, which seems to be unable to defend itself against excessive absorption of lime and thus experiences a dearth of potash which naturally interferes with the formation of starch and chlorophyl; hence probably induces the chlorosis so well known to occur on excessively calcareous soils. The lime-loving Corsican pine takes up a larger total amount of ash and more phosphoric acid, and nearly three times as much potash, but considerably less lime than did the maritime pine on the same calcareous soil.

The corresponding analyses made by Fliche and Grandeau, of the leaves and wood of chestnut grown on the same two kinds of soils, gave in general the same results; and they add that the smaller content of iron absorbed by the calcifuge trees when grown on calcareous soil point also to a deleterious influence upon the normal formation of chlorophyl.

Following Fliche and Grandeau, Bonnier made corroborative tests by sowing seeds of the same plants, both calciphile and calcifuge, upon the two kinds of soils, and noting the differences in their mode of growth and internal structure.

Bull. de la Société Botanique de France, tome 26, 1879.

Calciphile, Calcifuge and Silicophile plants.

The subject has been somewhat exhaustively discussed by Contejean who enumerates and has classified under the three general heads of calciphile, calcifuge and indifferent, over 1700 species of European plants. Unfortunately he had but few soil analyses at his disposal, and was inclined to consider as non-calcareous, most soils that gave no effervescence with acids. But notwithstanding this disadvantage so far as his contention of the efficacy of chemical soil-composition, and especially of lime is concerned, he disproves very effectually the physical theory of Thurmann, by numerous examples from France and elsewhere in Europe; and also disposes very definitely of the claim that there is a special class of “silicophile” plants. He concludes that silica (and sand) is merely a neutral and inert medium which offers refuge to the plants “expelled” by lime; and that clay similarly exerts no chemical but only a purely physical action. That potash, phosphoric acid and nitrogen, while most essential as plant-foods, exert otherwise little if any effect on general plant distribution. He alludes similarly to magnesia; and his final conclusion is that “chemical are in general more potent than physical influences,” and that the most widely active influences are carbonate of lime and chlorid of sodium. He does not, of course, deny the potent influence of moisture upon plant distribution.

Geographie botanique. Influence du terrain sur la vegetation. Baillère et Fils, Paris, 1881, 143 pp.

Since these publications were made, many observers have investigated the subject, and the broad distinction between lime-loving or calciphile and lime-repelled or calcifuge plants has been very generally recognized and discussed: but the cause of this discrimination by plants is still more or less the subject of controversy. Some still claim that the calcifuge plants (such as the chestnut, the huckleberries and whortle-berries, the heather and many other Ericaceæ, most sedges, etc.) are repelled by calcareous lands because they need a large supply of silica, which they suppose cannot well be assimilated in presence of much lime; hence they also designate the calcifuge plants as “silicophile”; while others attribute the preference of calciphile plants to the physical effects produced upon the soil by lime, as outlined above (chapter 20, page 379).

The contention that the presence of much lime in soils renders silica insoluble and hence unassimilable by plants, is at once negatived by the fact that waters exceptionally rich in silica, partly simply dissolved by carbonic acid, partly in the form of water-soluble alkali-silicates, are very abundantly found in the arid region. This is especially the case in California, where moreover a number of species of very rough-surfaced horsetail rushes and grasses prove the ready absorption of silica when wanted, even in strongly calcareous soils. But the question is whether the supposed class of silicophile plants is a reality or merely a theoretical fiction, based upon the habit of speaking of “siliceous” soils as a class apart from other and especially heavier or clay soils. As a matter of fact, the siliceous soils usually so called are simply those poor in clay and lime—in other words, “light” lands, the outcome of the weathering of quartzose rocks into sandy soils, which in the humid region are always poor in lime because thoroughly leached. In the arid region, on the contrary, sandy lands are quite commonly just as calcareous as the heavier soils, and show no “silicophile” flora.

According to the writer’s observations and views, it being obvious that some plants are practically indifferent to the presence or absence of lime in the soil except in so far as it influences favorably the physical conditions, moisture must always stand first as the condition of maximum crop production, and as a conditio sine qua non of the best development of plants on all kinds of soils; its best measure being a matter of special adaptation to each species. But this being understood, he agrees with Contejean as to the commanding influence of lime in determining the adaptation of soils to plants, both cultivated and wild. At the same time, it is obvious that the absence of the opportunity to observe really native vegetation, adapted to the soils through ages, has created for European observers difficulties which are readily solved where original native floras are available.

Schimper says pointedly that observations prove that the differences between the location of plants on calcareous and siliceous soils are not constant, but vary from province to province; that e. g., the list of indifferent (bodensteter) plants for the Alps do not hold good in the Dauphiné, still less between the Carpathians and Skandinavia. According to Wahlenberg the following species are calciphile in the Carpathians, and according to Christ indifferent in Switzerland: Dryas octopetala, Saxifraga oppositifolia, most of the leguminous species, Gentiana nivalis, G. tenella, G. verna, Erica carnea, Chamæorchis alpina, Carex capillaris. Geum reptans is reported by Bonnier to be exclusively calciphile on Mont Blanc, exclusively silicophile in the Dauphiné; indifferent in Switzerland. A great number of similar contradictions are reported by others as well, and the entire subject thus becomes rather vague; so that Schimper and others suggest that climatic conditions may in part be responsible for these discrepancies.

Pflanzengeographie, p. 111 & ff.

In all, or nearly all these cases, it is tacitly assumed that the underlying geological formation has essentially been the source of the soil, and that its character is determined accordingly. But this assumption is wholly arbitrary unless confirmed by actual direct examination. A soil-formation overlying limestone on the slopes of a range may be wholly derived from non-calcareous formations lying at a higher elevation, or may have been leached of its original lime-content by abundant rains. The feldspars constituting rocks designated as granite, may or may not be partially or wholly of the soda-lime instead of the potash series; the mica may or may not be partially replaced by hornblende, in which cases the soil would be calcareous to the extent of determining the character of the flora as calcifuge or calciphile, without its being at all evident in the physical character of the soil, which would still be “granitic” or “siliceous.” Such observations in order to be critically decisive, clearly require that the observer should be, not merely a systematic botanist, nor a mere geologist or chemist, but all these combined. There is good reason to believe that most or all of these supposed contradictions would disappear before a critical physical and chemical examination of both the soils and the rocks from which they are supposed to have been derived. Contejean himself, in placing so many of his long catalogue of plants into the doubtful groups, suggests many cases in which the above considerations may explain the apparent discrepancies.

What is a calcareous soil? The definition adopted for this volume has been given in a previous chapter (chapter 19, page 367); viz, that a soil must be considered calcareous so soon as it naturally supports a calciphile flora—the “lime vegetation” so often referred to above and named in detail. Upon this basis it has been seen that some (sandy) soils containing only a little over one-tenth of one per cent of lime show all the characters and advantages of calcareous soils; while in the case of heavy clay soils, as has been shown, the lime-percentage must rise to over one-half per cent to produce native lime growth. While in the United States observations of the contrasts between calciphile and calcifuge floras are easily made in the field, and the facts must attract the attention of any fairly qualified observer, in Europe they would have to be made the subject of special cultural investigation based upon soil analysis; a procedure not yet fully accredited abroad, any more than in the United States. In a general way it has however been recognized by Maercker, as shown at the end of the preceding chapter. How far this estimate was based upon American precedents, can now be only conjectured. Certain it is that the European definition of calcareous soils remains to the present day a wholly different one from that stated above; and from this have arisen the greater part of the doubts and differences of opinions among European botanists as to the classification of plants in relation to calcareous soils. Two per cent of lime (equivalent to nearly double the amount of carbonate) is the prevailing European postulate for a calcareous soil. Some go so far as to postulate effervescence with acids, requiring about 5% of the carbonate.

Predominance of Calcareous Formations in Europe.—It is not generally recognized even among geologists how abnormally predominant are limestone formations in Europe. In all works on European agriculture we find the “lime sand” mentioned as a normal ingredient of soils, specially provided for (or against) in the operations of soil examination. Its presence is the rule, its absence the exception. Soils as poor in lime as are those of the long-leaf and short-leaf pine regions of the United States, are there very exceptional and (like the “Haideböden” of northern Germany) have long remained almost uncultivated. Calcareous soils being the rule in the regions of intense culture, the ideas of both agriculturists and agricultural chemists have in Europe, in the main, been based upon them as normal soils; so that instead of comparing calcareous, and non-calcareous soils properly speaking—i. e., such as would not bear native lime-vegetation—the majority of comparisons has actually been made between soils which, in the American sense, were all or chiefly within the calcareous class. It is characteristic of this state of things that the injuriousness of an excess of lime is among the foremost themes of European (especially French and English) agricultural writers, as against the beneficent effects prominently assigned to lime in America. No such popular saying as that “a lime country is a rich country” exists in Europe; on the contrary, we constantly hear, and see in books, the mention of “poor chalk lands,” and in France especially the deleterious effects of excess of lime upon crops is the theme of remark. Excess of lime in their marly lands has been the despair of French vintners, and Viala was specially sent to America to find some vine to serve as a grafting stock which would resist the tendency to chlorosis which renders many of the American phylloxera-resistant vines useless to the viticulturists of France. Viala did not find such grapevines until he reached the cretaceous (chalk) area of Texas, where the native vines had long ago adapted themselves to marly soils; and these vines have solved the problem for French viticulture.

And England, France, Belgium and most of western Europe are rich countries, largely owing to their abundant limestone formations; and it may be questioned whether, had this been otherwise, Europe would so long have remained the center of civilization; for starving populations are not a good substratum for high mental culture and progress. It may equally be asked whether the invariably calcareous character of arid soils, as heretofore shown, has not, together with their general high quality, been largely a determining factor in the location and persistence of so many ancient civilizations in arid lands; as outlined in chapter 21, page 417. In this connection, the proper distinction between calcareous and non-calcareous soils passes from the domain of natural science to that of the history of human civilization.