For profusion of bloom and brilliancy of coloring, the land of the
tropics, with all its luxuriance of vegetation, can offer nothing to
compare with a New England meadow in June. Along the great rivers of
the South or in the islands of the East strange and beautiful flowers
occur individually or in small groups, but the traveler looks in vain
for myriads of blossoms giving a distinctive coloring to the landscape
itself. It was long the popular notion that the colors of flowers were
of no importance except as they gave human pleasure. This idea has
been made familiar by a well-known line of Gray's Elegy. It was a
German pastor, Christian Conrad Sprengel, at the close of the last
century, who first pointed out their true significance. So
enthusiastically did he pursue his botanical studies that he neglected
the duties of his office, and finally even omitted the Sunday sermon.
The natural result followed, that he was deprived of his parish. In
straitened circumstances he then sought unsuccessfully to maintain
himself at Berlin by giving lessons in botany and Sunday excursions in
search of plants. His book, now a botanical classic, attracted but
little attention; his publisher did not even send him a copy of it,
and in disgust he turned from the study of plants to that of
languages. The title of the work, The Secret of Nature in the Form and
Fertilization of Flowers Discovered, affords us the pleasure of
knowing that he rightly estimated the importance of his observations.
Sprengel clearly states that the bright hues of flowers, as is now
well established, serve as signals to attract the attention of
nectar-loving insects flying near by. He was led to this conclusion
very fitly by the study of _Myosotis_, the "forget-me-not." He has not
been forgotten. His name and theory were rescued from obscurity by
Darwin; his book a few years ago was reprinted at Leipsic, and is now
universally recognized, says H. Müller, as having "struck out a new
path in botanical science."
A day's stroll through the fields and woodlands is sufficient to show
that yellow and white blossoms are in Nature more common than red or
blue. From an examination of 741 New England and Eastern species
belonging to 48 families (see table) it appears that 164 are yellow,
283 white, 71 red, 136 blue and purple, and 87 green. Greenish flowers
occur in 25 families, yellow in 29, white in 32, red in 16, purple and
blue in 22.
_The Predominant Colors of the Flowers of Ranunculaceæ to Cornaceæ in
the Northern States._
--------------+---------+--------+--------+--------+---------+--------
| Yellow. | White. | Red. | Blue. | Green. | Total.
--------------+---------+--------+--------+--------+---------+--------
Ranunculaceæ | 19 | 19 | 2 | 14 | 6 | 60
Magnoliaceæ | 1 | 4 | .. | .. | 1 | 6
Anonaceæ | .. | .. | .. | 1 | .. | 1
Menispermaceæ | .. | 2 | .. | .. | 1 | 3
Berberaceæ | 2 | 3 | .. | .. | 1 | 6
Nymphæaceæ | 3 | 2 | .. | 1 | .. | 6
Sarraceniaceæ | 1 | .. | .. | 1 | .. | 2
Papaveraceæ | 4 | 2 | 2 | .. | .. | 8
Fumariaceæ | 2 | 3 | 2 | 1 | .. | 8
Cruciferæ | 17 | 37 | 2 | 5 | 4 | 65
Capparidaceæ | .. | 1 | .. | .. | .. | 1
Resedaceæ | 1 | .. | .. | .. | .. | 1
Violaceæ | 4 | 6 | .. | 8 | .. | 18
Cistaceæ | 4 | .. | .. | .. | 4 | 8
Droseraceæ | .. | 3 | 1 | .. | .. | 4
Hyperaceæ | 18 | .. | 2 | .. | .. | 20
Elatinaceæ | .. | .. | .. | .. | 1 | 1
Caryophyllaceæ| .. | 32 | 15 | .. | 6 | 53
Portulaceæ | 1 | .. | 3 | 1 | .. | 5
Malvaceæ | 5 | 4 | 10 | 3 | .. | 22
Tiliaceæ | .. | 2 | .. | .. | .. | 2
Camilliaceæ | .. | 2 | .. | .. | .. | 2
Linaceæ | 3 | .. | .. | 1 | .. | 4
Geraniaceæ | 3 | 2 | 2 | 6 | .. | 13
Rutaceæ | .. | 2 | .. | .. | 1 | 3
Anarcardiaceæ | 1 | .. | .. | .. | 5 | 6
Vitaceæ | .. | .. | .. | .. | 7 | 7
Rhamnaceæ | .. | 3 | .. | .. | 4 | 7
Celastraceæ | .. | .. | .. | 2 | 1 | 3
Sapindaceæ | 2 | 2 | 2 | .. | 5 | 11
Polygalaceæ | 2 | 3 | 4 | 5 | .. | 14
Leguminosæ | 19 | 28 | 6 | 61 | 2 | 116
Rosaceæ | 19 | 44 | 13 | 2 | 2 | 80
Calycanthaceæ | .. | .. | .. | 3 | .. | 3
Saxifragaceæ | 2 | 20 | .. | 1 | 13 | 36
Crassulaceæ | 2 | 3 | 1 | 2 | 1 | 9
Hammelaceæ | 1 | 1 | .. | .. | 1 | 3
Halorageæ | .. | .. | .. | .. | 9 | 9
Onagraceæ | 15 | 2 | 4 | 5 | 4 | 30
Melastomaceæ | .. | .. | .. | 3 | .. | 3
Lythraceæ | .. | 1 | .. | 8 | .. | 9
Loasaceæ | 1 | .. | .. | .. | .. | 1
Cactaceæ | 3 | 1 | .. | .. | .. | 2
Cucurbitaceæ | .. | 2 | .. | .. | 1 | 3
Umbelliferæ | 8 | 33 | .. | 2 | 2 | 45
Araliaceæ | .. | 3 | .. | .. | 3 | 6
Cornaceæ | .. | 11 | .. | .. | 2 | 13
|---------+--------+--------+--------+---------+--------
Total | 164 | 283 | 71 | 136 | 87 | 741
--------------+---------+--------+--------+--------+---------+--------
Yellow appears to have been the first color developed, and flowers
with this coloration are usually simple and regular in structure, as
the buttercups and five-fingers. But why, it will be asked, should
yellow have been the primitive color? The spores and spore-cases of
the club mosses, and the pollen of all cone-bearing trees, and, in
fact, of most plants, are yellow, and the yellow coloration of the
first petals is doubtless correlated with this fact. Flowers of this
tint are peculiarly attractive to yellow-banded flies, and when dull
are avoided by beetles. Yellow flowers vary greatly in size, but pale
yellow flowers are usually small, and bright or orange-yellow are
large. _Ranunculus abortivus_ and _R. sceleratus_, which grow in wet
places, are small and pale, while _R. bulbosus_ and _R. acris_, the
familiar buttercups of our meadows, are an inch broad. An apparent
exception to the above rule is offered by the globe-flower (_Trollius
laxus_), found in dense swamps, which has solitary, very large, pale
greenish-yellow flowers. As the cultivated European and Asiatic
species have bright yellow flowers, the coloring of the sepals of _T.
laxus_, for the petals are wanting, has probably retrograded from
growing in dense shade.
Yellow flowers in their natural state exhibit but little variation of
color. They change most readily to white, and less often to red or
blue. Under cultivation sudden variations from yellow to white have
been observed. A double yellow hollyhock, according to Darwin,
suddenly turned one year into a single white kind, and a chrysanthemum
has been seen to bear both yellow and white flowers. It will be
observed in the accompanying table that in all families in which
yellow flowers are common, white are also common, except in the
_Hyperaceæ_, which contain no white-flowered species. Some species of
mustard regularly fade to white, while many white flowers show that
they are descended from ancestral yellow forms by retaining vestiges
of this color on the base of the petals, as in the water-crowfoot. The
pale yellow flowers of _Oenothera laciniata_, of the cultivated _Ribes
aureum_, and of _Diervilla trifida_ in fading change to rose or red,
exhibiting a tendency to develop red coloration. _Aquilegia
canadensis_ produces scarlet flowers, which are yellow inside and
rarely all over. There are two other species in the Northern flora
which exhibit similar coloring, _Lonicera sempervirens_ and _Spigelia
marylandica_, and the former is sometimes yellow throughout.
_Myosotis_ is at first pale yellow, and changes to sky-blue. But the
best illustration of the transition from yellow to blue is exhibited
by the violet family; the smallest and simplest species is yellow, the
most highly specialized is blue, and all the intermediate stages are
presented by _Viola tricolor_.
Honey-guides are exceedingly rare among yellow flowers. _Cassia
chamæcrista_, which has nearly regular, showy yellow flowers, has two
or three petals with a purple spot at base, while four of the anthers
are yellow and six purple. It is interesting to compare with this
flower the change of color presented by _Arnebia_. When the flower
opens, each lobe of the yellow corolla is marked by a dark purple
spot, which soon begins to fade, and by the next day has entirely
disappeared. _Saxifraga aizoides_ has golden flowers spotted with
orange, and attracts a large number of insect visitors, and the yellow
violets have their petals marked with dark-brown lines leading to the
honey glands. Sulphur-yellow flowers are visited chiefly by
bumblebees, and their coloration seems to have been developed by their
selective influence from red or purple-flowered ancestors. Müller
observed that the sulphur-yellow flowers of _Sempervivum Wulfenii_,
which are unlike the primitive yellow of the _Crassulaceæ_, are purple
at base. This purple coloring he believed to be a remnant inherited
from an earlier purple-flowered form. _Hibiscus trionum_, which is
sulphur-yellow with a blackish eye, has perhaps been derived from a
red-flowered ancestor, for the three other species of the genus are
rose or flesh colored.
White flowers, in the opinion of the writer, are due to retrogression,
and are derived from yellow, red, or blue, and in some instances from
the primitive green, as in the involucre of _Cornus_. As a whole they
present no advance in specialization over yellow flowers, and are
often smaller and less conspicuous. When the petals of blossoms
containing yellow, red, or blue pigments are placed in concentrated
alcohol they turn to white. To produce these pigments is evidently
more or less a tax upon the energies of the plant, which, whenever
possible, is avoided. They are not present in the embryonic buds, and
may not develop until they are well advanced in size. In _Gentiana
crinita_ the yellowish-white bud is nearly an inch long before the
purple coloring appears, and the corolla always remains white at base.
A stimulus to the growth of the plant makes itself apparent in the
increased brilliancy of the flowers, as when they are exposed to clear
sunlight or are treated with nitrate of soda, and may also be observed
in the flushing of tulips, by which they lose their variegated colors
when treated with strong manure. On the other hand, a check in
nutrition and growth will cause a diminution of the perianth in size,
accompanied by retrogression in color. When double red poppies are
transplanted the whole plant is dwarfed, while the flowers are much
smaller and pure white. This view of the origin of white flowers
explains why they are the commonest in Nature, accounts for their
being most numerous in families in which yellow flowers are likewise
numerous, and why they are most true to name under cultivation. Many
white flowers also exhibit other evidences of degeneration in their
structure. Numerous species of _Cruciferæ_ and _Caryophyllaceæ_ have
small white flowers, which regularly fertilize themselves; and in
_Lepidium_, _Stellaria_, and _Sagina_ the petals are sometimes present
and in other instances are wanting.
White flowers often develop red or blue coloration. It is interesting
to note that the red and white varieties of the hyacinth were derived
from the wild blue form earlier than the yellow. Darwin gives an
instance of a white and red rose produced on the same root, also of
white and pink flowers on a single plant of _Antirrhinum majus_.
_Cratægus oxyacantha_, a dark pink hawthorn, has been known to throw
out a tuft of pure white blossoms. Every stage of the transition from
white to red is placed before us by the rose family. The thorns are
white, rarely tinged with rose; in the pear and apple the flowers are
white, regularly shaded with red; and one of the _Spiræas_ is rose,
rarely white, while in the roses proper the six species are
rose-colored, but the prairie rose changes to white. Under cultivation
the wild geranium has been seen to produce upon the same plant both
white and blue flowers. Good examples of the transition from white to
blue and from blue to white may be met with in the _Ranunculaceæ_ and
_Leguminosæ_. _Delphinium tricorne_ is bright blue, sometimes white,
_Viola canadensis_ has the petals white inside but the upper ones
tinged with violet beneath, _Astragalus_ has a part of the species
white and a part purple, while it is common to find blue and white
varieties of _Hepatica_ growing on the same grassy bank. White flowers
pass more readily into red, blue, or yellow than any one of these
colors can be converted into any other, since it is easier to develop
a new pigment than to transform one already existing. This is
confirmed by the experience of florists, who always seek to obtain a
white variety from which to develop the desired hue.
Red flowers are much rarer than blue, and both are seldom common in
the same family. For instance, in the pink family red and white
blossoms prevail, and there are no blue shades. The pinks are crimson
and scarlet, often with elegant markings and a strong aromatic odor.
The honey is deeply concealed, and they are visited almost exclusively
by butterflies and millers. Twenty-eight species of diurnal
_Lepidoptera_ have been collected upon a single variety of
_Saponaria_. Of the eighty species of _Rosaceæ_, thirteen are red and
two purple, but the forty-four white flowers are very generally tinged
or tipped with red. The two purplish-flowered species, _Geum rivale_
and _Potentilla palustris_, belong to genera in which yellow
predominates, and this primitive color is still evident in both their
calyx and corolla. There are no blue or violet flowers. This family
exhibits a marked tendency both in stem, leaf, bud, flower, and fruit
to develop reddish coloration, a tendency which is probably due to the
chemical constitution of the sap. There are no flowers in this family
adapted to _Lepidoptera_, but they are visited by a mixed company of
flies, beetles, and _Hymenoptera_. The smaller and less specialized
_Rosaceæ_ are yellow and white and are visited by a variety of
short-lipped insects. With the increase of the flower in size and
conspicuousness the number of insect visitors greatly increases, and
the enlargement of the flower is attended by red coloration. Owing to
the chemical constitution of the nutritive fluid, probably to its
acidity (for when the petals of a rose are treated with ammonia they
become blue), there has been no opportunity for the development of
blue coloration by insects. With the enlargement of the perianth and
the increased flow of sap, red tints have tended to appear by process
of oxidation.
The correlation of red coloring with an increased flow of sap is well
illustrated by the galls of the wild-rose tree, which are often "as
rosy as the rosiest apple." An abnormal flow of sap is caused to the
part stung by the insect, and red coloration is due to the action of
light, for it is of no service to the plant. Again, when the flowers
of _Cratægus coccinea_ are stung by the gall-fly the different organs
all become bright red, and the change in coloring is accompanied by an
increase in size. In some instances red colors, according to Darwin,
indicate greater vigor on the part of the plant, and I have also
observed that the dwarfing of red flowers under cultivation may cause
them to revert to white.
It was long, indeed, believed that the same species could not produce
yellow, red, and blue flowers. But this doctrine, to use the words of
Dr. Lindley, "must now be laid up in the limbo of pleasant dreams."
This supposed law is contradicted by the hyacinth, pansy, _Delphinium
cardinale_, and many other plants. Though red and blue coloring never
occurs among the roses, a hyacinth has been seen to produce a
perfectly pink and a perfectly blue blossom on the same truss, and the
_Borraginaceæ_ afford examples of flowers turning from red to blue in
even a short space of time.
Blue is the highest color of the floral world, and is preferred by
bees. Blue flowers are, as a rule, highly specialized both in form and
color, and often possess marvelous mechanisms which aid in
disseminating the pollen. This coloring is very common in the mint and
pulse families, and in this district there are in the former
forty-nine and in the latter sixty-one species of blue flowers. Their
structure is such that few insects besides the long-tongued bees can
gain access to the honey, and in some instances a single species of
flower is visited by a single kind of bee, as one of the larkspurs by
one of the bumblebees. While this high specialization of the flower
may insure intercrossing, it is yet open to many objections, such as
scarcity of proper guests, mechanical imperfections, perforation of
the flowers by bees, and development of the perianth at the expense of
the essential organs.
It is noteworthy that when genera occur containing three or more
species they are seldom all blue or purple; one species at least, and
frequently more than one, is yellow, white, or red. In _Trifolium_,
_T. pratense_ is rose-purple, _T. repens_ white, and _T. agrarium_
yellow. In the genus _Astragalus_ a part of the species are violet or
blue and a part white, and the same is true of _Lespedeza_ and
_Vicia_; in _Lathyrus_ three species are blue-purple, one yellow, and
one yellowish white. It is probably more advantageous in these genera
for a part of the species to be of one color and a part of another
than for all to be blue. When species are closely allied bees tend to
visit them indiscriminately, as has been observed to be true of the
buttercups, _Spiræas_, and golden-rods. During an afternoon the writer
carefully collected the insect visitors to _Solidago bicolor_, our
only cream-colored golden-rod. Both the number of species and of
individuals taken was much larger than upon the yellow-flowered and
more abundant varieties of this genus growing near by. There could be
no doubt that the whitish coloration was beneficial in enabling
insects to distinguish it more readily. Many purplish flowers are
regular, often showing indications of degeneration, are devoid of
honey, and are self-fertilized or adapted to _Diptera_, or, as in
_Hepatica_, which is visited by bees for the pollen, open to a wide
circle of visitors. In the sea purslane (_Sesuvium maritimum_), a
prostrate maritime herb, there are no petals, but the five-parted
calyx is purplish inside. The genus _Ammannia_ of the _Lythraceæ_ has
the petals small, purplish, and in one species they are wanting; the
axillary flowers of _Bracenia purpurea_ are small and dull purple; in
the common papaw the lurid purple flowers are large and adapted to
_Diptera_, as are probably the lurid purple flowers of _Calycanthus_.
Blue flowers may revert to red, white, or yellow. The fringed
_Polygala_ of Britain is usually bright blue, but often reverts to
pink and white; there is a pure white variety of the blue-eyed grass;
_Mertensia virginica_ is purple-blue, rarely white; the larkspur is
bright blue, sometimes white, and a white variety of the purple
_Trillium_ frequently occurs; there is, indeed, no improbability of a
white-flowered form of every species being discovered. _Viola
calcarata_ is normally blue, but sometimes changes to the ancestral
yellow.
The possession of a strong scent may, however, in many instances more
than compensate for the absence of color. This is well illustrated in
_Lepidium sativum_. The flowers are small and inconspicuous and in
rainy weather do not fully open, yet, as it is odoriferous, Müller
found it more abundantly visited by insects than any other crucifer.
It is their strong odor, rather than their color, that renders so many
umbellifers so attractive to a great variety of insects. Nocturnal
flowers, which are visited by moths, are usually white and
sweet-scented, though the evening primrose is yellow and _Saponaria
officinalis_ is rose-colored. Kohler and Schübeler have shown that a
larger proportion of white flowers are fragrant than of any other
color. Of 1,193 white flowers examined by them, 187 were odoriferous;
of 951 yellow, 75; of 923 red, 85; of 594 blue, 31. But neither color
nor odor will long alone serve to insure the visits of insects. The
common elderberry exhibits the disadvantages which may attend the want
of honey when there is but a limited supply of pollen. There are great
masses of odoriferous flowers which convert the shrub into a huge
bouquet, but it blooms at midsummer, when it must contend with many
nectar-yielding plants. As a result, it is almost wholly deserted by
insects. Only four species of flies have been taken upon it, and
repeatedly the blossoms were examined without discovering a single
visitor, and yet upon the jewel-weed and the red-osier cornel, a few
yards away, scores were at work.
* * * * *
Among the more recent applications of electricity is one for the
desiccation of wood, by the Nadon Bretonneau method, by which
wood is made as fit for use for certain exact processes in as
many months as it has formerly taken years. It is also proposed
by Mr. Shaw, an English mining engineer, to substitute water and
steam for gunpowder in mine blasts, a cartridge of water being
placed instead of the powder cartridge, and vaporized by passing
the electrical current through it.