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.
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, Pinus Pinaster. | Corsican Pine, Pinus Laricio. | ||
|---|---|---|---|
| On non- calcareous soil. | On calcareous soil. | On calcareous 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 |
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.