This is one of the most difficult and important subjects connected with
the study of plants. Before it can be well organized it will be
necessary to bring together very many more observations of plants in all
parts of the world than is possible now. However, a few facts are known
which are both interesting and suggestive. In order to make their
presentation as definite as possible, this paper will be restricted to a
brief account of the geographic distribution of seed plants.
One of the two great groups of seed plants is known as the Gymnosperms,
a group which in our region is represented by pines, spruces, hemlocks,
cedars, etc. In the tropics the group is represented by a very different
type of trees, known as the Cycads. They resemble in general habit
tree-ferns, or palms. The group of Gymnosperms with which we are
acquainted have been called Conifers on account of the very
characteristic cones which they bear. Several principles connected with
geographic distribution may be illustrated by considering briefly these
two groups of Gymnosperms.
The Cycads are absolutely restricted to the tropics, a few forms
reaching into semi-tropical conditions, as in southern Florida. If a
comparison be made between the eastern and western tropics, it will be
discovered that the Cycads are almost equally divided between the two
regions. For an unknown time, but certainly a very long one, these
eastern and western Cycads have been separated from one another. As a
consequence they have become so unlike that one kind of Cycad is never
found in both hemispheres. Their long separation from one another, and
their somewhat different conditions of living, have resulted in working
out differences of structures which botanists recognize as species,
genera, etc.
The Conifers, on the other hand, are characteristic of temperate
regions. If the distribution of Conifers were indicated upon a world
map, there would be shown a heavy massing of them in the northern region
and a lighter massing in the southern region, the two being separated
from one another by a broad tropical belt. This tropical belt is
traversed in just two places; one is by means of the East Indian bridge,
across which certain Australasian forms reach China and Japan; the other
is the chain of the Andes mountains, along which a single northern type
has worked its way into the southern part of South America. The two
great masses of Conifers, therefore, lie in the northern and southern
hemispheres, rather than in the eastern and western hemispheres, as is
the case with the Cycads. This long separation has resulted just as it
did with the Cycads; that is, the northern and southern Conifers are not
any longer alike, but differ so widely from one another that botanists
cannot discover any form which is common to both the northern and
southern hemispheres, excepting the single one already mentioned, which
has succeeded in crossing the tropics by means of the Andes bridge.
Another interesting fact in connection with the distribution of the
Conifers is that their great centers of display are in regions which
border the Pacific Ocean, and they have often been spoken of as a
Pacific group. There are three special centers of display; one is the
China-Japan region, a second is the general Australasian region, and the
third is western North America. Just why this border region of the
Pacific is especially favorable for this sort of plant life is a
question which we do not as yet pretend to answer. Another fact which
illustrates this persistent distribution in connection with the Pacific
is that in the case of the Conifers which belong to the southern
hemisphere, the continental masses which pair in the display of similar
forms are Australia and South America.
Another fact, which is true of all large groups, is that certain forms
have a very extensive distribution, and others are very much restricted
in their occurrence. For example, the greatest genus of Conifers is the
genus made up by the pines, at least seventy kinds of which are
recognized. This great genus sweeps throughout all the north temperate
regions of the globe. There is a similar extensive distribution of the
different kinds of spruce, larch, juniper, etc. On the other hand, the
giant redwood, known as Sequoia, is restricted to certain comparatively
small areas in California. In China and Japan, and also in Australia,
there are numerous illustrations of forms very much restricted in their
occurrence.
The other great group of seed plants is known as the Angiosperms, and to
it belong all those seed plants which are most commonly met in this
region. The distribution of Angiosperms is a very much more difficult
question than that of Gymnosperms; for while there are only about four
hundred kinds of living Gymnosperms, there are more than one hundred
thousand kinds of living Angiosperms. In presenting the distribution of
this great group, it will be necessary to consider its two main
divisions separately, for they differ from one another very much. One of
the groups is known as the Monocotyledons, to which belong such forms as
the grasses, lilies, palms, orchids, etc.
Some prominent facts in reference to the geographical distribution of
these Monocotyledons are as follows: They contain four great families,
which include almost one-half of their number, and which have become
world-wide in their distribution. These families are the grasses, the
sedges, the lilies, and the irises. This world-wide distribution means
that these families have succeeded in adapting themselves to every
condition of soil and climate. In this world-distribution the grasses
easily lead, not only among Monocotyledons, but among all seed plants.
Another fact in reference to the Monocotyledons is that they include an
unusual number of families which are entirely aquatic in their habit.
These aquatic families are also world-wide in their distribution, so far
as fresh and brackish waters can be called world-wide. It is important
to notice that while the world-families which belong to the land have
worked out about ten thousand different forms, the world-families which
belong to the water have worked out considerably less than two hundred
different forms. This seems to indicate that the great number in the one
case is due to the very diverse conditions of the land, while the small
number in the latter case is due to the very uniform conditions of water
life.
A third fact of importance is that the Monocotyledons are mainly massed
in the tropics, and in this sense are almost an exact contrast to the
Conifers we have been considering above. The same effect of separation
in working out diversity in structure is shown by the Monocotyledons as
was shown by the eastern and western Cycads, and the northern and
southern Conifers. For example, the palms represent the great tree group
of Monocotyledons, and are restricted to the tropics as rigidly as are
the Cycads. They are found in about equal numbers in the eastern and
western tropics, but there are no forms in common. The eastern and
western forms have become so different that they might almost be
regarded as different families.
The Monocotyledons are also somewhat famous for the number of air plants
which they contain—that is, plants which have sometimes been called
“perchers,” because they fasten themselves upon trunks and branches and
supports of various kinds, and absorb what they need directly from the
air. It is a notable fact that these so-called “perchers” are very much
more abundant in the western tropics than in the eastern. An explanation
for this is to be found in the fact that the western tropics have a very
much greater rainfall; in fact, in the rainy woods of the Amazon region
the air is saturated with water, and everything is dripping.
One of the facts in connection with the distribution of Monocotyledons
is quite puzzling, and that is the very poor representation of the whole
group in the southern hemisphere. In examining the distribution of other
groups in the southern hemisphere, it is found that Australia and its
general vicinity is prolific in peculiar forms. In the case of the
Monocotyledons, however, the Australasian region is the most
poverty-stricken one in all the southern hemisphere. Just why the
southern hemisphere in general, and the Australasian region in
particular, are unfavorable for Monocotyledons, it is hard to say. Of
course in these cases the world-families already mentioned are
represented.
The other great division of Angiosperms is known as Dicotyledons, which
include such forms as our common forest trees, buttercups, roses, peas,
mints, sunflowers, etc. As there are about eighty thousand of these
Dicotyledons, it is impossible to state anything very definite in
reference to the distribution of the group as a whole. Taking the higher
forms, however, as representing the general tendency of the group, some
of the facts of distribution are as follows:
It has been noticed that the Monocotyledons are massed in the tropics,
and that the temperate and boreal regions have been left comparatively
free by previous groups, with the exception of the Conifers, which only
develop tree types. With the coming of the Dicotyledons, therefore, the
vast temperate and boreal regions presented a particularly favorable
field, which they have entered and taken possession of. This vast group
is prominently adapted to living in the unoccupied temperate and boreal
regions. This does not mean that they are not found in the tropics for
they hold their own there with the other groups.
Dicotyledons, however, succeeded in working out but three
world-families: Composites, to which the sunflowers, dandelions, etc.,
belong; the Mints; and the Plantains. There are other large families
which characterize certain great areas, but they are not world-wide in
their distribution.
Another fact, which might indicate that the Dicotyledons have taken
possession of comparatively unoccupied regions only, is that they are
very poorly represented, so far as higher groups are concerned, in
aquatic conditions. It would seem as though the conditions of life in
the water had been fairly well taken up by other groups. In looking over
the display of Dicotyledons in the tropics of the eastern and western
hemispheres, it becomes evident that there is no such difference between
the forms of the two regions as in the groups previously mentioned. It
will be remembered, however, that in the case of the Cycads and palms,
which were used as illustrations, they are restricted to the tropics,
and their eastern and western forms are separated from one another, not
merely by oceans, but by temperate and boreal lands. In the case of
Dicotyledons this is different, for while they are found in the tropics,
they are found in the other regions as well, and have better chances for
intermingling than the other groups.
This tropical display of Dicotyledons further shows the great prominence
of America in the display of forms. This appears not merely in the
greater number of peculiar forms and often families which appear in
tropical America; but whenever the continents are paired in the display
of forms, America is always one of the pair, Asia or Africa being the
other member.
It will be recognized from what has been said that the whole subject of
geographic distribution is a very extensive one, and that it will be a
long time before the important facts are recorded. The importance of the
subject rests not so much upon the mere presence of certain plants in
certain regions, but it has to do with explaining just why the
conditions are suited to the plants, and also just how the plants have
come to be what they are and where they are.
John Merle Coulter.
[Illustration: ]
Description of Plate—A, flowering twig; 1, 2, 3, corolla; 4, 5,
pistil; 6, 7, stamen; 9, pollen; 10, 11, fruit; 12, 13, seed.
VANILLA.
(_Vanilla planifolia_, Andrews.)
You flavor everything; you are the _vanille_ of society.
—Sydney Smith: Works, p. 329.
Vanilla planifolia belongs to the Orchid family (Orchidaceae), though it
has many characteristics not common to most members of the family. It is
a fleshy, dark-green perennial climber, adhering to trees by its aerial
roots, which are produced at the nodes. The stem attains a length of
many feet, reaching to the very tops of the supporting trees. The young
plant roots in the ground, but as the stem grows in length, winding
about its support and clinging to it by the aerial roots, it loses the
subterranean roots and the plant establishes itself as a saprophyte or
partial parasite, life habits common to orchids. The leaves are entire,
dark-green, and sessile. Inflorescence consists of eight to ten flowers
sessile upon axillary spikes. The flowers are a pale greenish yellow,
perianth rather fleshy and soon falls away from the ovary or young
fruit, which is a pod, and by the casual observer would be taken for the
flower stalk. The mature fruit is a brown curved pod six to eight inches
long, smooth, splitting lengthwise in two unequal parts, thus liberating
the numerous, very small, oval or lenticular seeds.
There are several species of vanilla indigenous to Eastern Mexico,
growing in warm, moist, shaded forests. It is now extensively cultivated
in Mexico; also in Mauritius, Bourbon, Madagascar and Java. It is
extensively grown in hot-houses of England and other temperate
countries. The wild growing plants no doubt depended upon certain
insects for pollination, but with the cultivated plants this is effected
artificially by means of a small brush.
The word vanilla is derived from the Spanish vainilla, the diminutive of
vaina, meaning a sheath or pod, in reference to the fruit. There is
little doubt that the natives of Mexico employed vanilla as a flavor for
cocoa long before the discovery of America. We received our first
description of the plant from the Spanish physician Hernandez, who,
during 1571-1577 explored New Spain or Mexico. In 1602, Morgan,
apothecary to Queen Elizabeth, sent specimens of the fruit to Clusius,
who described it independently of Hernandez. In 1694 vanilla was
imported to Europe by way of Spain. In France it was much used for
flavoring chocolate and tobacco. During the first half of the eighteenth
century it was extensively used in Europe, particularly in England,
after which it seems to have gradually disappeared. Now it is, however,
again very abundantly employed in nearly all countries.
Vanilla must be cultivated with great care. In Mexico a clearing is made
in the forest, leaving a few trees twelve to fifteen feet apart to serve
as a support for the vanilla plants. Cuttings of the vanilla stems are
made three to five feet in length, one cutting being inserted into the
soil to a depth of about ten inches near each tree. The cuttings become
rooted in about one month and grow quite rapidly, but do not begin to
bear fruit until the third year and continue to bear for about thirty
years. In Reunion, Mauritius and the Seychelles the young plants are
supported by a rude trellis fastened between the trunks of trees. In
cultivation pollination is universally effected artificially; the pollen
being transplanted from one flower to another by means of a small brush
or pencil. Only the finest flowers are thus fertilized so as to prevent
exhaustion and to insure a good commercial article. Among wild growing
plants pollination is effected through the agency of insects, which
evidently do not occur in the vicinity of the plantations; thus man is
called upon to assist nature. The pods are cut off separately as they
ripen; if over-ripe they are apt to split in drying; if collected green
the product will be of an inferior quality.
The peculiar fragrance of the vanilla pods is due to vanillin, which
occurs upon the exterior of the dried fruit in the form of a crystalline
deposit, which serves as a criterion of quality. This substance does not
pre-exist in the ripe fruit. It is developed in the process of drying
and fermentation. In Mexico the collected pods are placed in heaps under
a shed until they begin to wilt or shrivel, whereupon they are subjected
to the sweating process conducted as follows: The pods are wrapped in
woolen cloth and exposed to the sun during the day or heated in an oven
at 140°F., then enclosed in air-tight boxes at night to sweat. In
twenty-four to thirty-six hours they assume a chestnut-brown color. They
are then dried in the sun for several months.
In Reunion the pods are first scalded for a few minutes in boiling hot
water, then exposed to the sun for about one week, wrapped in woolen
blankets; then spread out and dried under sheds, turning frequently so
as to insure uniform drying. When the pods can be twisted around the
finger without splitting or cracking the “smoothing process” begins.
This consists in rolling the pods between the fingers to distribute the
unctuous liquid, which exudes during the sweating process
(fermentation), and to which the pods owe their lustre and suppleness.
Vanilla workers are apt to suffer from an affection known as vanillism,
characterized by an itching eruption of the skin, nasal catarrh, more or
less headache and muscular pain. By some this is said to be caused by a
poisonous substance in the vanilla or perhaps the oil of cashew, with
which the pods are coated. According to others the trouble, at least the
itching and eruption, is caused by a species of acarus (itch mite) found
upon the pod. It must also be borne in mind that most of these workers
are anything but cleanly in their habits. Bacteria, dirt, etc., find
their way to the pods from the dirty hands of the workmen. The entire
process of gathering, sweating, drying, smoothing and packing, as
carried on in Mexico and South American countries is not conducted in
accordance with recognized sanitary rules.
There are a number of commercial varieties of vanilla named after the
countries in which they are grown or after the centers of export, as
Mexican, Vera Cruz, Bourbon, Mauritius, Java, La Guayra, Honduras and
Brazilian vanilla. The most highly valued Mexican variety is known as
Vainilla de leg (leg, meaning law). The pods are long, dark-brown, very
fragrant and coated with crystals. Since vanilla is a costly article
adulteration is quite common. Useless pods are coated with balsam of
Peru to give them a good appearance. Split, empty pods are filled with
some worthless material, glued together and coated with balsam of Peru.
Vanillin also occurs in Siam benzoin, in raw beet-sugar and in cloves.
It has been artificially prepared from coniferin, a substance found in
the sap-wood of fir-trees, and from asafoetida. In Germany commercial
vanilla is now largely prepared from eugenol, a constituent of oil of
cloves.
Vanillin seems to have some special action upon the nervous system, and
has been employed in the treatment of hysteria. It is also used to
disguise disagreeable tastes and odors of medicines, as in lozenges and
mixtures. Its principal use is that of spice for flavoring chocolate,
confectionery, ices, ice-cream, drinks, pastry; in the preparation of
perfumery, sachet powders, etc. It has a very pleasant, delicate aroma
when properly diluted and can be very effectively combined with other
odors. Vanilla, combined with almonds, simulates heliotrope.
The poisonous effects of ice creams flavored with vanilla are perhaps
not due to vanillin, but to toxins formed by bacteria found upon vanilla
pods, or the bacteria of the milk and cream used.
Albert Schneider.