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.[193] 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.
[193] 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.[194]
[194] 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,[195] 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.
[195] 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,[196] 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.
[196] 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[197] 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
-----------------+-----------------+-------------+--------------
[197] 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[198] 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.
[198] Bull. de la Société Botanique de France, tome 26, 1879.
_Calciphile, Calcifuge and Silicophile plants._
The subject has been somewhat exhaustively discussed by Contejean[199]
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.
[199] 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[200] 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.
[200] 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.