has its leaves crowded and divided into three linear lobes, some of
which are again divided. In this the plant differs very greatly from
its allies; it has, however, acquired a very striking resemblance
to a species of Euphorbia, abundant on the Riviera. The acrid juice
of the Euphorbias secures them immunity against a host of enemies.
As the two plants grow together there is little room to doubt that,
like the dead-nettle, the bugle profits by its likeness to its well
protected neighbor.
The rare heath Menziesia cærulia, thought to be protected by its
marked resemblance to the crowberry (Empetrum nigrum), has also been
adduced as a probable case of mimicry.
Mr. A. R. Wallace in _Tropical Nature_ refers to the stone
mesembryanthemum at the Cape described by Dr. Burchell, which closely
resembles in form and color the stones among which it grows; on this
account the discoverer believes this juicy little plant generally
escapes the notice of cattle and wild herbivorous animals.
Mr. J. P. Mansel Weale mentions that in Karoo many plants have
tuberous roots above the soil resembling stones so perfectly that it
is almost impossible to distinguish them. The tubers of the potato
itself in its native home may perhaps be protected in this way.
The last-mentioned observer has also noted a labiate plant, Ajuga
orphrydis, in South Africa, which bears a strong resemblance to an
orchid. As this is the only species of bugle in the district, Mr.
Wallace thinks the flower profits by the mimicry and succeeds in
attracting the insects required for its fertilization. A species
of balsam at the Cape has also acquired an orchid-like aspect;
Tillandsia Usneoides, one of the pineapple family, grows on trees
in tropical America, and has a resemblance to a shaggy lichen so
marked that it is generally mistaken for a plant of that order. The
fly agaric, our most conspicuously colored fungus, according to
Dr. Plowright, is closely imitated by a parasitic flowering plant,
Balanophora volucrata, the scarlet cap, the dotted warts, the white
stem and volva being all accurately represented.
The curious shapes of some exotic orchids are probably advantageous
from their resemblance to insects and birds. One of our native
orchids, Listua ovata, has a flower which in shape decidedly
resembles a species of beetle, Grammoptera lævis, by which it is
fertilized. Perhaps in this case the insect mimics the flower, as
certainly happens with a pink-colored mantis in Java, which so
exactly resembles a pink orchid that butterflies are attracted to it
in mistake. The insect is carnivorous, and lies in wait for its prey,
which is easily secured by the help of this strange disguise. Mutual
resemblances of this description are rather characteristic of the
Orchidaceæ. From their resemblance, real or fanciful, to butterflies,
moths, bees, spiders, etc., various species of Habenaria, Neotinea,
and Ophrys derive their names--the butterfly, spider, bee and
fly orchises. In the orchid Ophrys muscifera are two little
protuberances, regarded by the late H. Müller as pseudo-nectaries.
Of this class of deceptive contrivances, however, we have a better
example in Parnassia palustris, one of the saxifrages. This flower
has five fan-like scales alternating with the stamens; the margins
of the scales are fringed with hair-like processes, and each hair
is capped with what appears to be a drop of honey. These are really
hard, dry knobs, but so much do they resemble drops of honey that
flies lick them before discovering the imposture. The intention of
these sham nectar-drops may either be to decoy unprofitable guests
from the real nectar, of which a limited supply is produced in the
hollow of each scale, or to advertise it for the benefit of the more
intelligent visitors.
Somewhat analogous to these pseudo-nectaries are the greenish
swellings which arise on the veins of the petals of Eremurus. These
little swellings present a striking resemblance to aphides, or
plant-lice, and Kerner states that a fly accustomed to hunt after
aphides pierces and sucks the swellings, apparently mistaking them
for the insects.
Relations which remind us of the pink orchid and mantis, mentioned
above, seem to exist between the little bladders of Utricularia and
the entomostracans. The bladderwort is a carnivorous plant with small
submerged vesicles in which minute insects and entomostracans are
caught. In shape these little traps of Utricularia are not unlike the
body of a crustacean; the stalk corresponds to the tail, and near
the entrance of each bladder are several antenna-like filaments so
resembling certain appendages of the crustaceans that they impart
to the structure a ludicrous resemblance to such an entomostracan
as Daphne. This curious likeness was remarked by Mr. Darwin and can
hardly be altogether accidental; perhaps the prey is more readily
induced to approach the snare by reason of the resemblance. Here
also may be mentioned the imposture practiced on its victims by
Darlingtonia, another insectivorous plant. In the hood of its
pitcher-like leaf are several transparent spaces through which the
light shines into the interior; to these the imprisoned flies are
attracted and thereby diverted from the only opening through which
escape is possible. Mistaking the “windows” for real openings, the
captives exhaust themselves in vain efforts to regain their liberty
and are ultimately precipitated into the depths of the pitcher.
The flowers of the ox-eye daisy and the feverfew are very much
alike, and this was adduced by the late Mr. Grant Allen as a possible
case of mimicry. But the probability is that in this instance
the resemblance is merely homomorphic. The colors of flowers are
distinctive as well as attractive. Where two species of plant
grow together and are in blossom at the same time it is to their
disadvantage to have the flowers of the one mistaken for those of
the other. To secure cross-fertilization it is needful that the
insect visitors pass from one flower to another of the same species,
otherwise the pollen will be conveyed to the stigmas of the wrong
species. It is of importance that the fertilizing agents should be
able readily to distinguish different flowers, and this is no doubt
one reason for the diversity of their colors, shapes, and odors.
This circumstance must operate as a check against the production
of mimetic blossoms; it will not, however, prevent flowers from
acquiring a likeness to any object other than a flower.
Mimetic resemblances are much more numerous among fruits and seeds
than in flowers. A very curious example is Orphicaryon paradoxum, the
snake-nut of Demerara, inside which is the coiled embryo resembling a
small snake. Among others mentioned by Lord Avebury are Tricosanthes
anguina, the pod of which assumes a snake-like guise; Scorpiurus
vermiculata, with pods in the form of a worm or caterpillar; S.
subvillosa and Biserrula pelecinus, where the resemblance is to a
centipede and certain lupines with spider-like seeds. The seeds of
Abrus precatorius, Martynia diandra, Jatropha, the castor oil plant
and the scarlet runner mimic certain beetles. The presence of a
caruncle representing the head of the insect renders the imitation
more complete; this structure takes no part in germination, and
Kerner is of opinion that it prevents the ants from attacking the
substance of the seeds which they drag about from place to place.
The ox-tongue and cow-wheat have worm-like seeds, and several plants
have fruit difficult to distinguish from little pieces of dry twig.
The jet-black, shining seeds and achenes of Delphinium, Helleborus,
Juncus, Atriplex, Polygonum, etc., are easily mistaken for beetles;
the brightly colored seeds of Iris Germanica are also in all
probability mimetic.
The beautiful glossy scarlet and black piebald seeds of Abrus known
as rosary beans perhaps escape destruction through birds mistaking
them for some nauseous insect gaudily attired in warning colors. But
from the manner in which the seed-vessels of Iris and Arbus dehisce
and expose their seeds the brilliant colors of the latter would
appear to subserve dissemination rather than protection. Such hard
seeds are probably dispersed through the agency of insectivorous
birds, which seize them in mistake for their more legitimate prey.
According to Lord Avebury, the beans of Abrus mimic the beetle
Artemis circumusta. The smaller seeds, known as crab’s eyes, are
colored in an analogous manner. These cases are the less surprising
if we have regard to the fact that the majority of dry fruits,
though green while growing, become black or brown when they fall
to the ground, so that their general tint corresponds with their
surroundings and tends to concealment.
The odors of fungi are very varied. Clathrus and Phallus are
offensive and attract swarms of blow-flies; Lactarius and Hydnum, on
the other hand, are sweetly scented like the flowers of Melilotus.
Among the odors of fungi enumerated by Dr. Plowright are those of
aniseed, mint, peppermint, garlic, horse-radish, cucumber, ripe
apricots, rotting pears, rancid herring, Russia leather, gas-tar,
prussic acid, nitric acid, and cacodyl. Like the hemlock, Agaricus
incanus has the smell of mice, two species of Lactarius have the
odor of the common house-bug, while Hygrophorus cossus smells like
the larvæ of the goat-moth. Fifteen or sixteen species of agaric
resemble oatmeal both in taste and smell, Hydnum repandum has the
flavor of oysters, recalling the oyster plant among the Boraginaceæ,
whose leaves have a similar taste. Several are possessed of a
nut-like flavor. The common stinkhorn, Phallus impudicus, is the
best known representative of a large family of fungi, the members of
which are found in various parts of the world. The Phalloidi include
Phallus, Lysurus, Simblum, Clathrus, Aseröe, and other genera, all
characterized by offensive odors and conspicuous colors. These fungi
have been carefully studied by Mr. T. Wemys Fulton, whose paper on
the _Dispersion of Spores in Fungi_ in the _Annals of Botany_ for
1899 contains many interesting and important observations bearing on
mimicry.
The rapid elongation of the stinkhorn is very remarkable; the fungus
has been observed to attain a height of several inches in half an
hour, furnishing an apt illustration of the proverb that ill weeds
grow apace. It not only emits an intolerable charnel-house stench,
but its ghastly pallid hue seen against the background of its usual
surroundings is peculiarly suggestive of the dead carcass of some
animal. Its surface at first exudes a sweetish slime containing
sugar, but the hymeneum or spore-bearing portion is deliquescent
and the entire mass speedily undergoes a series of changes, the
white becoming brown, then black, the solid mass being ultimately
resolved into a dark fetid fluid in which the spores are suspended.
These mimetic changes, which so closely approximate to those
of decomposition, attract carrion flies in prodigious numbers.
Blow-flies even deposit their eggs on the fungus, and the maggots
seem to develop as though nourished by its substance. On examination
Mr. Fulton found the spores adhering in thousands to the feet and
proboscides of the insects. Their excrement he found to consist
almost entirely of spores, and the latter were found by experiment
to be still capable of germination. There is therefore no doubt in
this case that flies are employed as agents in the dispersion of the
fungus. This statement also applies to various Coprini and others
with a deliquescent hymeneum.
Quite a number of flowers have distinctly mimetic odors. It can
hardly be doubted, for example, that the offensive smell of the
carrion flowers Stapelia, Aristolochia, Arum, Rafflesia, and others,
is more effective in promoting cross-fertilization because of its
resemblance to the odor of putrid meat. So completely are the flesh
flies deceived that they often deposit their eggs on the petals of
carrion flowers.
Fetid odors occur in Bryonia, Helleborus, Geranium, Stachys, Ballota,
Iris and other genera. The odors of others have a curious resemblance
to the smells emitted by certain animals. Hypericum hircinum and
Orchis hircina are bad smelling flowers with an odor resembling that
of the goat; Coriandrum sativum has the fetid smell of bugs, while
the hemlock, again, emits a strong odor of mice. Along with these may
be mentioned Adoxa, the musk orchis, the grape hyacinth, and other
musky-scented flowers.
The resemblance in smell between these flowers and the secretion
formed in the scent glands of the musk ox and other animals is,
to say the least, a remarkable coincidence. Possibly flies which
accompany cattle may be attracted by smells of this description. Very
curious also is the vinous smell of Œnanthe, and the brandy-like
aroma of the yellow water lily Nuphar, hence called the brandy
bottle. Ethereal oils exhaled by plants while attractive to some
animals seem to repel others; the scents of sweet-smelling flowers
such as Daphne, Thymus, Marjoram, Melilotus, and Gymnademia,
though grateful to bees and butterflies, appear to be distasteful
to ruminants. Kerner states that in general the latter avoid all
blossoms; even caterpillars do not readily attack the petals of their
food plants. Odor may therefore be protective or attractive or it
may be of use in both ways. The same remark applies to color, which
may serve either to attract or repel; the richly variegated leaves
of the Indian nettles--species of Colleus--and the tinted foliage
of begonia and geranium may possibly escape injury on account of
the general resemblance to colored blossoms. Instances in which
one plant resembles another in smell are not very common in the
flowering class, though cases do occur like the garlic, mustard and
apple-scented Salvia. Resembling odors are much more frequent among
fungi.
Characteristic examples of homomorphism are seen in the resemblances
which many species of Euphorbia present to the cactus tribe and
in the pollen-masses of the orchids and asclepias. In Britain the
order Euphorbiaceæ is represented by the box, dog’s-mercury, and
the sun-spurges, but many foreign species have quite a different
appearance and agree with the cacti in their aborted leaves and green
succulent stems. The globular, columnar, and angular forms give to
both a peculiar aspect by which they are broadly distinguished from
all other vegetable types; and yet in systematic position these two
orders stand far apart. The nearest affinities of the Euphorbiæ
are with the Urticaceæ and other orders having incomplete flowers,
while the nearest allies of the Cacti are the Cucurbitaceæ and other
calycifloral orders. Succulent stemmed plants of this description are
specially adapted to an arid climate, and it is not unreasonable to
suppose that the similarity between the Euphorbiæ and Cacti results
from the long-continued action of similar external conditions upon
similarly endowed tissues.
The Australian Casuarinas are dicotyledons with incomplete
flowers nearly related to the oak, hazel, and other Cupuliferæ,
but in outward appearance they have a singular resemblance to
the horsetails, a family of cryptogams. One of the gymosperms
or cone-bearing class, Ephedra, also presents the same jointed
appearance so characteristic of Equisetaceæ. Growing in marshy
places very like those affected by Equisetum we find the mare’s-tail
Hippurus, a flowering plant allied to the fuchsia family, but
externally resembling Equisetum in its jointed stem and whorled
leaves. A familiar instance of the same kind of homomorphism is
Equisetum sylvaticum, which might almost be described as a liliputian
fir-tree. The little flowers of the water ranunculus look exactly
like miniature water lilies, while the leaves and flowers of Caltha
palustris simulate the yellow Nuphar so much that in some parts
of the country the marsh marigold is known as the water lily. The
specific name of another aquatic, Lymnanthemum nymphædides, indicates
a peculiarity of the same kind. Leaf analogies are frequent among
aquatic plants; the orbicular, peltate leaf of the Indian cress
occurs, for example, in Hydrocotyle, Nelumbium, and others. The
brown color and translucence of Potamogeton, Myriophyllum, and other
aquatics assimilates them to the fronds of Laminaria and other
sea-weeds.
A grass-like habit is assumed by some plants. This character is
attained in the meadow vetchling by the arrested development of
the compound leaves and the great elongation of the stipules.
Lathyrus nissolia has the stipules minute, but the phyllodes or
leaf-like petioles impart the grass-like character. A moss-like
habit occurs in a great many plants belonging to very different
families; thus the wiry stem of the purging flax reminds one of
the seta of Polytrichum. The pearlwort of the walls, many alpine
saxifrages, pinks, and gentians present very much the appearance of
mosses, _e. g._, Silene acaulis, Saxifraga bryoides, S. hypnoides,
Arenaria Cherleri, etc. The sub-species Saxifraga geum is another
instance of leaf analogy. The generic name Pyrola implies a fancied
resemblance of the leaves to those of the pear tree. Certain
leaf-types frequently recur, the rough broadly tongue-shaped leaf of
the bugloss, for example; hence the very common specific appellation
echioides. The nettle-leaved bell-flower reproduces the foliage of
Urtica and the sinuate leaf of the oak appears in several families.
Parasitic phanerogams like Rafflesia commonly exhibit the fungoid
character in a marked degree. In their internal structure, coloring,
spore-like seeds and other characters they approximate closely to the
fungi.
As examples of homomorphism between closely allied plants may be
mentioned the false oat, which so strikingly resembles the cultivated
species, and the barren strawberry, which agrees so closely with the
cultivated strawberry of our gardens.
Although it is only under exceptional circumstances that a
flower is likely to mimic another blossom closely, vague general
resemblances are not uncommon, such as that between the rock-rose
and the buttercup, between the milkwort and the vetch, and between
Veronica and Valerianella. A more decided likeness is that of the
garden annual Collinsia to the butterfly blossoms of the pea tribe.
This case is peculiarly instructive since the homomorphism can
be traced to its cause. The butterfly-like corolla of Leguminosæ
seems to have afforded the pattern after which a number of flowers
have been fashioned. The Papilionaceæ are adapted to bees rather
than to butterflies or moths, and the pollen is applied to the
ventral surface of the insect, the essential organs being lodged
in the carina or pouch formed by the two lower petals. Among the
Scrophulariaceæ to which Collinsia belongs, the pollen is commonly
sprinkled on the back of the insect and the stamens are contained in
the upper lip of the corolla; Collinsia is, however, exceptional; the
stamens are lodged within the lower lip of the flower and the pollen
is applied to the ventral surface of the bee. Here the resemblance
is evidently an indirect result brought about by the flowers of
Collinsia having become adapted to the same class of visitors as the
Papilionaceæ, viz., bees which have their brushes or baskets of hair
for collecting pollen attached to the abdomen. Where two flowers are
very like insects are apt to mistake the one species for the other,
but this will not involve any loss if there is an interval between
their periods of blossoming.
Homomorphic likenesses are not confined to homologous organs; an
organ of one plant sometimes exhibits a perfect resemblance to a
different organ on some other plant. Thus Aristolochia sipho, the
Dutchman’s pipe, so-called from the appearance of its flowers, has
a perianth singularly like the leaf-pitchers of Nepenthes, and the
curious little nectaries of Nigella might almost be compared with the
pitchers of the Australian insectivorous plant Cephalotus. As the
Aristolochias imprison small dipterous insects in their flowers these
instances favor to some extent Henslow’s idea that both flowers and
pitchers have arisen by hypertrophy caused through the irritation set
up by insects.
The homomorphism of the orchids and asclepiads is especially
interesting because of the objection to the Darwinian theory that it
presents; the coincidence is certainly unfavorable to the notion of
fortuitous variation. The orchids and asclepiads agree in producing
pollinia or pollen-packets which attach themselves to the bodies of
insects and are thus transferred from flower to flower. Although the
two flowers differ greatly in the details of their structure, this
curious contrivance occurs in no other plants, and yet the two orders
are as widely separated as it is possible to conceive. The orchids
belong to the petaloid division of Monocotyledons; the asclepias to
the gamopetalous Dicotyledons, with their nearest allies among the
Apocynaceæ, of which Vinca, the periwinkle, is perhaps the best known
representative. Although agreeing in this one particular, the flowers
are in other respects very dissimilar.
Another contrivance for promoting cross-fertilization met with in
unallied plants is the mouse-trap arrangement of hairs by means
of which small flies are temporarily imprisoned. This arrangement
occurs in Aristolochia, in species of Arum, and in Ceropegia, one
of the asclepiads. In these plants, where the affinities are so
slight, the mechanism for fertilization must in each case have arisen
independently.
THE BAMBOO AND PLANT GROWTH
--R. CAMPER DAY
If the many families of flowering plants were arranged in the order
of their utility to man or in the order of their abundance, the first
place in the list would unquestionably be assigned to the great
family of grasses. Of their omnipresence and abundance some idea may
be obtained from the fact that at least four thousand different kinds
have been described, and a German naturalist has estimated that they
constitute a twenty-second part of all known plants. Their utility
as food producers becomes obvious as soon as we recall the names of
rice, wheat, barley, oats, rye, and Indian corn, and remember how
large a proportion of our food is made from their seeds. Most of
these civilized and somewhat unnatural grasses have been so long
under cultivation, and so much altered by man’s selection, that
they are totally unfitted to shift for themselves, and would soon
become extinct if brought into competition with wild plants. The fact
that the wild forms from which they are descended can not now be
identified with certainty shows that their cultivation must date from
the very earliest ages. Rice alone is said to furnish more sustenance
to the human race than any other single species; the common meadow
grasses, such as the purple-tipped Anthoxanthum, which fills the
fields with its penetrating fragrance when the hay is newly mown, are
almost the only food of sheep and cattle; and those tall and sturdy
canes whose juice we squeeze out between rollers, and clarify and
crystallize into sugar, are only modified stems of grass.