LIFE.
SLIGHT MODIFICATIONS IN PLANTS FROM THE DEFINITE ACTION OF CHANGED
CONDITIONS, IN SIZE, COLOUR, CHEMICAL PROPERTIES, AND IN THE STATE OF
THE TISSUES—LOCAL DISEASES—CONSPICUOUS MODIFICATIONS FROM CHANGED
CLIMATE OR FOOD, ETC—PLUMAGE OF BIRDS AFFECTED BY PECULIAR NUTRIMENT,
AND BY THE INOCULATION OF POISON—LAND-SHELLS—MODIFICATIONS OF ORGANIC
BEINGS IN A STATE OF NATURE THROUGH THE DEFINITE ACTION OF EXTERNAL
CONDITIONS—COMPARISON OF AMERICAN AND EUROPEAN TREES—GALLS—EFFECTS OF
PARASITIC FUNGI—CONSIDERATIONS OPPOSED TO THE BELIEF IN THE POTENT
INFLUENCE OF CHANGED EXTERNAL CONDITIONS—PARALLEL SERIES OF
VARIETIES—AMOUNT OF VARIATION DOES NOT CORRESPOND WITH THE DEGREE OF
CHANGE IN THE CONDITIONS—BUD-VARIATION—MONSTROSITIES PRODUCED BY
UNNATURAL TREATMENT—SUMMARY.
If we ask ourselves why this or that character has been modified under
domestication, we are, in most cases, lost in utter darkness. Many
naturalists, especially of the French school, attribute every
modification to the “monde ambiant,” that is, to changed climate, with
all its diversities of heat and cold, dampness and dryness, light and
electricity, to the nature of the soil, and to varied kinds and amount
of food. By the term definite action, as used in this chapter, I mean
an action of such a nature that, when many individuals of the same
variety are exposed during several generations to any particular change
in their conditions of life, all, or nearly all the individuals, are
modified in the same manner. The effects of habit, or of the increased
use and disuse of various organs, might have been included under this
head; but it will be convenient to discuss this subject in a separate
chapter. By the term indefinite action I mean an action which causes
one individual to vary in one way and another individual in another
way, as we often see with plants and animals after they have been
subjected for some generations to changed conditions of life. But we
know far too little of the causes and laws of variation to make a sound
classification. The action of changed conditions, whether leading to
definite or indefinite results, is a totally distinct consideration
from the effects of selection; for selection depends on the
preservation by man of certain individuals, or on their survival under
various and complex natural circumstances, and has no relation whatever
to the primary cause of each particular variation.
I will first give in detail all the facts which I have been able to
collect, rendering it probable that climate, food, etc., have acted so
definitely and powerfully on the organisation of our domesticated
productions, that new sub-varieties or races have been thus formed
without the aid of selection by man or nature. I will then give the
facts and considerations opposed to this conclusion, and finally we
will weigh, as fairly as we can, the evidence on both sides.
When we reflect that distinct races of almost all our domesticated
animals exist in each kingdom of Europe, and formerly even in each
district of England, we are at first strongly inclined to attribute
their origin to the definite action of the physical conditions of each
country; and this has been the conclusion of many authors. But we
should bear in mind that man annually has to choose which animals shall
be preserved for breeding, and which shall be slaughtered. We have also
seen that both methodical and unconscious selection were formerly
practised, and are now occasionally practised by the most barbarous
races, to a much greater extent than might have been anticipated. Hence
it is difficult to judge how far differences in the conditions between,
for instance, the several districts in England, have sufficed to modify
the breeds which have been reared in each. It may be argued that, as
numerous wild animals and plants have ranged during many ages
throughout Great Britain, and still retain the same character, the
difference in conditions between the several districts could not have
modified in a marked manner the various native races of cattle, sheep,
pigs, and horses. The same difficulty of distinguishing between the
effects of natural selection and the definite action of external
conditions is encountered in a still higher degree when we compare
closely allied species inhabiting two countries, such as North America
and Europe, which do not differ greatly in climate, nature of soil,
etc., for in this case natural selection will inevitably and rigorously
have acted during a long succession of ages.
Prof. Weismann has suggested[1] that when a variable species enters a
new and isolated country, although the variations may be of the same
general nature as before, yet it is improbable that they should occur
in the same proportional numbers. After a longer or shorter period, the
species will tend to become nearly uniform in character from the
incessant crossing of the varying individuals; but owing to the
proportion of the individuals varying in different ways not being the
same in the two cases, the final result will be the production of two
forms somewhat different from one another. In cases of this kind it
would falsely appear as if the conditions had induced certain definite
modifications, whereas they had only excited indefinite variability,
but with the variations in slightly different proportional numbers.
This view may throw some light on the fact that the domestic animals
which formerly inhabited the several districts in Great Britain, and
the half wild cattle lately kept in several British parks, differed
slightly from one another; for these animals were prevented from
wandering over the whole country and intercrossing, but would have
crossed freely within each district or park.
From the difficulty of judging how far changed conditions have caused
definite modifications of structure, it will be advisable to give as
large a body of facts as possible, showing that extremely slight
differences within the same country, or during different seasons,
certainly produce an appreciable effect, at least on varieties which
are already in an unstable condition. Ornamental flowers are good for
this purpose, as they are highly variable, and are carefully observed.
All floriculturists are unanimous that certain varieties are affected
by very slight differences in the nature of the artificial compost in
which they are grown, and by the natural soil of the district, as well
as by the season. Thus, a skilful judge, in writing on Carnations and
Picotees[2] asks “where can Admiral Curzon be seen possessing the
colour, size, and strength which it has in Derbyshire? Where can
Flora’s Garland be found equal to those at Slough? Where do
high-coloured flowers revel better than at Woolwich and Birmingham? Yet
in no two of these districts do the same varieties attain an equal
degree of excellence, although each may be receiving the attention of
the most skilful cultivators.” The same writer then recommends every
cultivator to keep five different kinds of soil and manure, “and to
endeavour to suit the respective appetites of the plants you are
dealing with, for without such attention all hope of general success
will be vain.” So it is with the Dahlia:[3] the Lady Cooper rarely
succeeds near London, but does admirably in other districts; the
reverse holds good with other varieties; and again, there are others
which succeed equally well in various situations. A skilful gardener[4]
states that he procured cuttings of an old and well-known variety
(pulchella) of Verbena, which from having been propagated in a
different situation presented a slightly different shade of colour; the
two varieties were afterwards multiplied by cuttings, being carefully
kept distinct; but in the second year they could hardly be
distinguished, and in the third year no one could distinguish them.
The nature of the season has an especial influence on certain varieties
of the Dahlia: in 1841 two varieties were pre-eminently good, and the
next year these same two were pre-eminently bad. A famous amateur[5]
asserts that in 1861 many varieties of the Rose came so untrue in
character, “that it was hardly possible to recognise them, and the
thought was not seldom entertained that the grower had lost his tally.”
The same amateur[6] states that in 1862 two-thirds of his Auriculas
produced central trusses of flowers, and such trusses are liable not to
keep true; and he adds that in some seasons certain varieties of this
plant all prove good, and the next season all prove bad; whilst exactly
the reverse happens with other varieties. In 1845 the editor of the
‘Gardener’s Chronicle’[7] remarked how singular it was that this year
many Calceolarias tended to assume a tubular form. With Heartsease[8]
the blotched sorts do not acquire their proper character until hot
weather sets in; whilst other varieties lose their beautiful marks as
soon as this occurs.
Analogous facts have been observed with leaves: Mr. Beaton asserts[9]
that he raised at Shrubland, during six years, twenty thousand
seedlings from the Punch Pelargonium, and not one had variegated
leaves; but at Surbiton, in Surrey, one-third, or even a greater
proportion, of the seedlings from this same variety were more or less
variegated. The soil of another district in Surrey has a strong
tendency to cause variegation, as appears from information given me by
Sir F. Pollock. Verlot[10] states that the variegated strawberry
retains its character as long as grown in a dryish soil, but soon loses
it when planted in fresh and humid soil. Mr. Salter, who is well known
for his success in cultivating variegated plants, informs me that rows
of strawberries were planted in his garden in 1859, in the usual way;
and at various distances in one row, several plants simultaneously
became variegated; and what made the case more extraordinary, all were
variegated in precisely the same manner. These plants were removed, but
during the three succeeding years other plants in the same row became
variegated, and in no instance were the plants in any adjoining row
affected.
The chemical qualities, odours, and tissues of plants are often
modified by a change which seems to us slight. The Hemlock is said not
to yield conicine in Scotland. The root of the _Aconitum napellus_
becomes innocuous in frigid climates. The medicinal properties of the
Digitalis are easily affected by culture. As the _Pistacia lentiscus_
grows abundantly in the South of France, the climate must suit it, but
it yields no mastic. The Laurus sassafras in Europe loses the odour
proper to it in North America.[11] Many similar facts could be given,
and they are remarkable because it might have been thought that
definite chemical compounds would have been little liable to change
either in quality or quantity.
The wood of the American Locust-tree (_Robinia_) when grown in England
is nearly worthless, as is that of the Oak-tree when grown at the Cape
of Good Hope.[12] Hemp and flax, as I hear from Dr. Falconer, flourish
and yield plenty of seed on the plains of India, but their fibres are
brittle and useless. Hemp, on the other hand, fails to produce in
England that resinous matter which is so largely used in India as an
intoxicating drug.
The fruit of the Melon is greatly influenced by slight differences in
culture and climate. Hence it is generally a better plan, according to
Naudin, to improve an old kind than to introduce a new one into any
locality. The seed of the Persian Melon produces near Paris fruit
inferior to the poorest market kinds, but at Bordeaux yields delicious
fruit.[13] Seed is annually brought from Thibet to Kashmir[14] and
produces fruit weighing from four to ten pounds, but plants raised next
year from seed saved in Kashmir give fruit weighing only from two to
three pounds. It is well known that American varieties of the Apple
produce in their native land magnificent and brightly-coloured fruit,
but these in England are of poor quality and a dull colour. In Hungary
there are many varieties of the kidney-bean, remarkable for the beauty
of their seeds, but the Rev. M.J. Berkeley[15] found that their beauty
could hardly ever be preserved in England, and in some cases the colour
was greatly changed. We have seen in the ninth chapter, with respect to
wheat, what a remarkable effect transportal from the north to the south
of France, and conversely, produced on the weight of the grain.
When man can perceive no change in plants or animals which have been
exposed to a new climate or to different treatment, insects can
sometimes perceive a marked change. A cactus has been imported into
India from Canton, Manilla Mauritius, and from the hot-houses of Kew,
and there is likewise a so-called native kind which was formerly
introduced from South America; all these plants belong to the same
species and are alike in appearance, but the cochineal insect
flourishes only on the native kind, on which it thrives
prodigiously.[16] Humboldt remarks[17] that white men “born in the
torrid zone walk barefoot with impunity in the same apartment where a
European, recently landed, is exposed to the attacks of the _Pulex
penetrans._” This insect, the too well-known chigoe, must therefore be
able to perceive what the most delicate chemical analysis fails to
discover, namely, a difference between the blood or tissues of a
European and those of a white man born in the tropics. But the
discernment of the chigoe is not so surprising as it at first appears;
for according to Liebig[18] the blood of men with different
complexions, though inhabiting the same country, emits a different
odour.
Diseases peculiar to certain localities, heights, or climates, may be
here briefly noticed, as showing the influence of external
circumstances on the human body. Diseases confined to certain races of
man do not concern us, for the constitution of the race may play the
more important part, and this may have been determined by unknown
causes. The Plica Polonica stands, in this respect, in a nearly
intermediate position; for it rarely affects Germans, who inhabit the
neighbourhood of the Vistula, where so many Poles are grievously
affected; neither does it affect Russians, who are said to belong to
the same original stock as the Poles.[19] The elevation of a district
often governs the appearance of diseases; in Mexico the yellow fever
does not extend above 924 metres; and in Peru, people are affected with
the _verugas_ only between 600 and 1600 metres above the sea; many
other such cases could be given. A peculiar cutaneous complaint, called
the _Bouton d’Alep,_ affects in Aleppo and some neighbouring districts
almost every native infant, and some few strangers; and it seems fairly
well established that this singular complaint depends on drinking
certain waters. In the healthy little island of St. Helena the
scarlet-fever is dreaded like the Plague; analogous facts have been
observed in Chili and Mexico.[20] Even in the different departments of
France it is found that the various infirmities which render the
conscript unfit for serving in the army, prevail with remarkable
inequality, revealing, as Boudin observes, that many of them are
endemic, which otherwise would never have been suspected.[21] Any one
who will study the distribution of disease will be struck with surprise
at what slight differences in the surrounding circumstances govern the
nature and severity of the complaints by which man is at least
temporarily affected.
The modifications as yet referred to are extremely slight, and in most
cases have been caused, as far as we can judge, by equally slight
differences in the conditions. But such conditions acting during a
series of generations would perhaps produce a marked effect.
With plants, a considerable change of climate sometimes produces a
conspicuous result. I have given in the ninth chapter the most
remarkable case known to me, namely, that of varieties of maize, which
were greatly modified in the course of only two or three generations
when taken from a tropical country to a cooler one, or conversely. Dr.
Falconer informs me that he has seen the English Ribston-pippin apple,
a Himalayan oak, Prunus and Pyrus, all assume in the hotter parts of
India a fastigiate or pyramidal habit; and this fact is the more
interesting, as a Chinese tropical species of Pyrus naturally grows
thus. Although in these cases the changed manner of growth seems to
have been directly caused by the great heat, we know that many
fastigiate trees have originated in their temperate homes. In the
Botanic Gardens of Ceylon the apple-tree[22] “sends out numerous
runners under ground, which continually rise into small stems, and form
a growth around the parent-tree.” The varieties of the cabbage which
produce heads in Europe fail to do so in certain tropical
countries.[23] The _Rhododendron ciliatum_ produced at Kew flowers so
much larger and paler-coloured than those which it bears on its native
Himalayan mountain, that Dr. Hooker[24] would hardly have recognised
the species by the flowers alone. Many similar facts with respect to
the colour and size of flowers could be given.
The experiments of Vilmorin and Buckman on carrots and parsnips prove
that abundant nutriment produces a definite and inheritable effect on
the roots, with scarcely any change in other parts of the plant. Alum
directly influences the colour of the flowers of the Hydrangea.[25]
Dryness seems generally to favour the hairiness or villosity of plants.
Gärtner found that hybrid Verbascums became extremely woolly when grown
in pots. Mr. Masters, on the other hand, states that the _Opuntia
leucotricha_ “is well clothed with beautiful white hairs when grown in
a damp heat, but in a dry heat exhibits none of this peculiarity.”[26]
Slight variations of many kinds, not worth specifying in detail, are
retained only as long as plants are grown in certain soils, of which
Sageret[27] gives some instances from his own experience. Odart, who
insists strongly on the permanence of the varieties of the grape,
admits[28] that some varieties, when grown under a different climate or
treated differently, vary in a slight degree, as in the tint of the
fruit and in the period of ripening. Some authors have denied that
grafting causes even the slightest difference in the scion; but there
is sufficient evidence that the fruit is sometimes slightly affected in
size and flavour, the leaves in duration, and the flowers in
appearance.[29]
There can be no doubt, from the facts given in the first chapter, that
European dogs deteriorate in India, not only in their instincts but in
structure; but the changes which they undergo are of such a nature,
that they may be partly due to reversion to a primitive form, as in the
case of feral animals. In parts of India the turkey becomes reduced in
size, “with the pendulous appendage over the beak enormously
developed.”[30] We have seen how soon the wild duck, when domesticated,
loses its true character, from the effects of abundant or changed food,
or from taking little exercise. From the direct action of a humid
climate and poor pasture the horse rapidly decreases in size in the
Falkland Islands. From information which I have received, this seems
likewise to be the case to a certain extent with sheep in Australia.
Climate definitely influences the hairy covering of animals; in the
West Indies a great change is produced in the fleece of sheep, in about
three generations. Dr. Falconer states[31] that the Thibet mastiff and
goat, when brought down from the Himalaya to Kashmir, lose their fine
wool. At Angora not only goats, but shepherd-dogs and cats, have fine
fleecy hair, and Mr. Ainsworth[32] attributes the thickness of the
fleece to the severe winters, and its silky lustre to the hot summers.
Burnes states positively[33] that the Karakool sheep lose their
peculiar black curled fleeces when removed into any other country. Even
within the limits of England, I have been assured that the wool of two
breeds of sheep was slightly changed by the flocks being pastured in
different localities.[34] It has been asserted on good authority[35]
that horses kept during several years in the deep coal-mines of Belgium
become covered with velvety hair, almost like that on the mole. These
cases probably stand in close relation to the natural change of coat in
winter and summer. Naked varieties of several domestic animals have
occasionally appeared; but there is no reason to believe that this is
in any way related to the nature of the climate to which they have been
exposed.[36]
It appears at first sight probable that the increased size, the
tendency to fatten, the early maturity and altered forms of our
improved cattle, sheep, and pigs, have directly resulted from their
abundant supply of food. This is the opinion of many competent judges,
and probably is to a great extent true. But as far as form is
concerned, we must not overlook the more potent influence of lessened
use on the limbs and lungs. We see, moreover, as far as size is
concerned, that selection is apparently a more powerful agent than a
large supply of food, for we can thus only account for the existence,
as remarked to me by Mr. Blyth, of the largest and smallest breeds of
sheep in the same country, of Cochin-China fowls and Bantams, of small
Tumbler and large Runt pigeons, all kept together and supplied with
abundant nourishment. Nevertheless there can be little doubt that our
domesticated animals have been modified, independently of the increased
or lessened use of parts, by the conditions to which they have been
subjected, without the aid of selection. For instance, Prof.
Rütimeyer[37] shows that the bones of domesticated quadrupeds can be
distinguished from those of wild animals by the state of their surface
and general appearance. It is scarcely possible to read Nathusius’s
excellent ‘Vorstudien’[38] and doubt that, with the highly improved
races of the pig, abundant food has produced a conspicuous effect on
the general form of the body, on the breadth of the head and face, and
even on the teeth. Nathusius rests much on the case of a purely bred
Berkshire pig, which when two months old became diseased in its
digestive organs, and was preserved for observation until nineteen
months old; at this age it had lost several characteristic features of
the breed, and had acquired a long, narrow head, of large size
relatively to its small body, and elongated legs. But in this case and
in some others we ought not to assume that, because certain characters
are lost, perhaps through reversion, under one course of treatment,
therefore that they were at first directly produced by an opposite
treatment.
In the case of the rabbit, which has become feral on the island of
Porto Santo, we are at first strongly tempted to attribute the whole
change—the greatly reduced size, the altered tints of the fur, and the
loss of certain characteristic marks—to the definite action of the new
conditions to which it has been exposed. But in all such cases we have
to consider in addition the tendency to reversion to progenitors more
or less remote, and the natural selection of the finest shades of
difference.
The nature of the food sometimes either definitely induces certain
peculiarities, or stands in some close relation with them. Pallas long
ago asserted that the fat-tailed sheep of Siberia degenerate and lose
their enormous tails when removed from certain saline pastures; and
recently Erman[39] states that this occurs with the Kirgisian sheep
when brought to Orenburgh.
It is well known that hemp-seed causes bullfinches and certain other
birds to become black. Mr. Wallace has communicated to me some much
more remarkable facts of the same nature. The natives of the Amazonian
region feed the common green parrot (_Chrysotis festiva,_ Linn.) with
the fat of large Siluroid fishes, and the birds thus treated become
beautifully variegated with red and yellow feathers. In the Malayan
archipelago, the natives of Gilolo alter in an analogous manner the
colours of another parrot, namely, the _Lorius garrulus,_ Linn., and
thus produce the _Lori rajah_ or King-Lory. These parrots in the Malay
Islands and South America, when fed by the natives on natural vegetable
food, such as rice and plaintains, retain their proper colours. Mr.
Wallace has, also, recorded[40] a still more singular fact. “The
Indians (of S. America) have a curious art by which they change the
colours of the feathers of many birds. They pluck out those from the
part they wish to paint, and inoculate the fresh wound with the milky
secretion from the skin of a small toad. The feathers grow of a
brilliant yellow colour, and on being plucked out, it is said, grow
again of the same colour without any fresh operation.”
Bechstein[41] does not entertain any doubt that seclusion from light
affects, at least temporarily, the colours of cage-birds.
It is well known that the shells of land-mollusca are affected by the
abundance of lime in different districts. Isidore Geoffroy
Saint-Hilaire[42] gives the case of _Helix lactea,_ which has recently
been carried from Spain to the South of France and to the Rio Plata,
and in both countries now presents a distinct appearance, but whether
this has resulted from food or climate is not known. With respect to
the common oyster, Mr. F. Buckland informs me that he can generally
distinguish the shells from different districts; young oysters brought
from Wales and laid down in beds where “_natives_” are indigenous, in
the short space of two months begin to assume the “native” character.
M. Costa[43] has recorded a much more remarkable case of the same
nature, namely, that young shells taken from the shores of England and
placed in the Mediterranean, at once altered their manner of growth and
formed prominent diverging rays, like those on the shells of the proper
Mediterranean oyster. The same individual shell, showing both forms of
growth, was exhibited before a society in Paris. Lastly, it is well
known that caterpillars fed on different food sometimes either
themselves acquire a different colour or produce moths differing in
colour.[44]
It would be travelling beyond my proper limits here to discuss how far
organic beings in a state of nature are definitely modified by changed
conditions. In my ‘Origin of Species’ I have given a brief abstract of
the facts bearing on this point, and have shown the influence of light
on the colours of birds, and of residence near the sea on the lurid
tints of insects, and on the succulency of plants. Mr. Herbert
Spencer[45] has recently discussed with much ability this whole subject
on general grounds. He argues, for instance, that with all animals the
external and internal tissues are differently acted on by the
surrounding conditions, and they invariably differ in intimate
structure. So again the upper and lower surfaces of true leaves, as
well as of stems and petioles, when these assume the function and
occupy the position of leaves, are differently circumstanced with
respect to light, etc., and apparently in consequence differ in
structure. But, as Mr. Herbert Spencer admits, it is most difficult in
all such cases to distinguish between the effects of the definite
action of physical conditions and the accumulation through natural
selection of inherited variations which are serviceable to the
organism, and which have arisen independently of the definite action of
these conditions.
Although we are not here concerned with the definite action of the
conditions of life on organisms in a state of nature, I may state that
much evidence has been gained during the last few years on this
subject. In the United States, for instance, it has been clearly
proved, more especially by Mr. J. A. Allen, that, with birds, many
species differ in tint, size of body and of beak, and in length of
tail, in proceeding from the North to the South; and it appears that
these differences must be attributed to the direct action of
temperature.[46] With respect to plants I will give a somewhat
analogous case: Mr. Meehan,[47] has compared twenty-nine kinds of
American trees with their nearest European allies, all grown in close
proximity and under as nearly as possible the same conditions. In the
American species he finds, with the rarest exceptions, that the leaves
fall earlier in the season, and assume before their fall a brighter
tint; that they are less deeply toothed or serrated; that the buds are
smaller; that the trees are more diffuse in growth and have fewer
branchlets; and, lastly, that the seeds are smaller—all in comparison
with the corresponding European species. Now considering that these
corresponding trees belong to several distinct orders, and that they
are adapted to widely different stations, it can hardly be supposed
that their differences are of any special service to them in the New
and Old worlds; and if so such differences cannot have been gained
through natural selection, and must be attributed to the long continued
action of a different climate.
_Galls._—Another class of facts, not relating to cultivated plants,
deserves attention. I allude to the production of galls. Every one
knows the curious, bright-red, hairy productions on the wild rose-tree,
and the various different galls produced by the oak. Some of the latter
resemble fruit, with one face as rosy as the rosiest apple. These
bright colours can be of no service either to the gall-forming insect
or to the tree, and probably are the direct result of the action of the
light, in the same manner as the apples of Nova Scotia or Canada are
brighter coloured than English apples. According to Osten Sacken’s
latest revision, no less than fifty-eight kinds of galls are produced
on the several species of oak, by Cynips with its sub-genera; and Mr.
B. D. Walsh[48] states that he can add many others to the list. One
American species of willow, the _Salix humilis,_ bears ten distinct
kinds of galls. The leaves which spring from the galls of various
English willows differ completely in shape from the natural leaves. The
young shoots of junipers and firs, when punctured by certain insects,
yield monstrous growths resembling flowers and fir-cones; and the
flowers of some plants become from the same cause wholly changed in
appearance. Galls are produced in every quarter of the world; of
several sent to me by Mr. Thwaites from Ceylon, some were as
symmetrical as a composite flower when in bud, others smooth and
spherical like a berry; some protected by long spines, others clothed
with yellow wool formed of long cellular hairs, others with regularly
tufted hairs. In some galls the internal structure is simple, but in
others it is highly complex; thus M. Lacaze-Duthiers[49] has figured in
the common ink-gall no less than seven concentric layers, composed of
distinct tissue, namely, the epidermic, sub-epidermic, spongy,
intermediate, and the hard protective layer formed of curiously
thickened woody cells, and, lastly, the central mass, abounding with
starch-granules on which the larvæ feed.
Galls are produced by insects of various orders, but the greater number
by species of Cynips. It is impossible to read M. Lacaze-Duthiers’
discussion and doubt that the poisonous secretion of the insect causes
the growth of the gall; and every one knows how virulent is the poison
secreted by wasps and bees, which belong to the same group with Cynips.
Galls grow with extraordinary rapidity, and it is said that they attain
their full size in a few days;[50] it is certain that they are almost
completely developed before the larvae are hatched. Considering that
many gall-insects are extremely small, the drop of secreted poison must
be excessively minute; it probably acts on one or two cells alone,
which, being abnormally stimulated, rapidly increase by a process of
self-division. Galls, as Mr. Walsh[51] remarks, afford good, constant,
and definite characters, each kind keeping as true to form as does any
independent organic being. This fact becomes still more remarkable when
we hear that, for instance, seven out of the ten different kinds of
galls produced on _Salix humilis_ are formed by gall-gnats
(_Cecidomyidæ_) which “though essentially distinct species, yet
resemble one another so closely that in almost all cases it is
difficult, and in most cases impossible, to distinguish the full-grown
insects one from the other.”[52] For in accordance with a wide-spread
analogy we may safely infer that the poison secreted by insects so
closely allied would not differ much in nature; yet this slight
difference is sufficient to induce widely different results. In some
few cases the same species of gall-gnat produces on distinct species of
willows galls which cannot be distinguished; the _Cynips fecundatrix,_
also, has been known to produce on the Turkish oak, to which it is not
properly attached, exactly the same kind of gall as on the European
oak.[53] These latter facts apparently prove that the nature of the
poison is a more powerful agent in determining the form of the gall
than the specific character of the tree which is acted on.
As the poisonous secretion of insects belonging to various orders has
the special power of affecting the growth of various plants; as a
slight difference in the nature of the poison suffices to produce
widely different results; and lastly, as we know that the chemical
compounds secreted by plants are eminently liable to be modified by
changed conditions of life, we may believe it possible that various
parts of a plant might be modified through the agency of its own
altered secretions. Compare, for instance, the mossy and viscid calyx
of a moss-rose, which suddenly appears through bud-variation on a
Provence-rose, with the gall of red moss growing from the inoculated
leaf of a wild rose, with each filament symmetrically branched like a
microscopical spruce-fir, bearing a glandular tip and secreting
odoriferous gummy matter.[54] Or compare, on the one hand, the fruit of
the peach, with its hairy skin, fleshy covering, hard shell and kernel,
and on the other hand one of the more complex galls with its epidermic,
spongy, and woody layers, surrounding tissue loaded with starch
granules. These normal and abnormal structures manifestly present a
certain degree of resemblance. Or, again, reflect on the cases above
given of parrots which have had their plumage brightly decorated
through some change in their blood, caused by having been fed on
certain fishes, or locally inoculated with the poison of a toad. I am
far from wishing to maintain that the moss-rose or the hard shell of
the peach-stone or the bright colours of birds are actually due to any
chemical change in the sap or blood; but these cases of galls and of
parrots are excellently adapted to show us how powerfully and
singularly external agencies may affect structure. With such facts
before us, we need feel no surprise at the appearance of any
modification in any organic being.
I may, also, here allude to the remarkable effects which parasitic
fungi sometimes produce on plants. Reissek[55] has described a Thesium,
affected by an Œcidium, which was greatly modified, and assumed some of
the characteristic features of certain allied species, or even genera.
Suppose, says Reissek, “the condition originally caused by the fungus
to become constant in the course of time, the plant would, if found
growing wild, be considered as a distinct species or even as belonging
to a new genus.” I quote this remark to show how profoundly, yet in how
natural a manner, this plant must have been modified by the parasitic
fungus. Mr. Meehan[56] also states that three species of Euphorbia and
_Portulaca olereacea,_ which naturally grow prostrate, become erect
when they are attacked by the Œcidium. _Euphorbia maculata_ in this
case also becomes nodose, with the branchlets comparatively smooth and
the leaves modified in shape, approaching in these respects to a
distinct species, namely, the _E. hypericifolia._
_Facts and Considerations opposed to the belief that the
Conditions of Life act in a potent manner in causing definite
Modifications of Structure_
I have alluded to the slight differences in species naturally living in
distinct countries under different conditions; and such differences we
feel at first inclined to attribute, probably often with justice, to
the definite action of the surrounding conditions. But it must be borne
in mind that there exist many animals and plants which range widely and
have been exposed to great diversities of climate, yet remain uniform
in character. Some authors, as previously remarked, account for the
varieties of our culinary and agricultural plants by the definite
action of the conditions to which they have been exposed in the
different parts of Great Britain; but there are about 200 plants[57]
which are found in every single English county; and these plants must
have been exposed for an immense period to considerable differences of
climate and soil, yet do not differ. So, again, some animals and plants
range over a large portion of the world, yet retain the same character.
Notwithstanding the facts previously given on the occurrence of highly
peculiar local diseases and on the strange modifications of structure
in plants caused by the inoculated poison of insects, and other
analogous cases; still there are a multitude of variations—such as the
modified skull of the niata ox and bulldog, the long horns of Caffre
cattle, the conjoined toes of the solid-hoofed swine, the immense crest
and protuberant skull of Polish fowls, the crop of the pouter-pigeon,
and a host of other such cases—which we can hardly attribute to the
definite action, in the sense before specified, of the external
conditions of life. No doubt in every case there must have been some
exciting cause; but as we see innumerable individuals exposed to nearly
the same conditions, and one alone is affected, we may conclude that
the constitution of the individual is of far higher importance than the
conditions to which it has been exposed. It seems, indeed, to be a
general rule that conspicuous variations occur rarely, and in one
individual alone out of millions, though all may have been exposed, as
far as we can judge, to nearly the same conditions. As the most
strongly marked variations graduate insensibly into the most trifling,
we are led by the same train of thought to attribute each slight
variation much more to innate differences of constitution, however
caused, than to the definite action of the surrounding conditions.
We are led to the same conclusion by considering the cases, formerly
alluded to, of fowls and pigeons, which have varied and will no doubt
go on varying in directly opposite ways, though kept during many
generations under nearly the same conditions. Some, for instance, are
born with their beaks, wings, tails, legs, etc., a little longer, and
others with these same parts a little shorter. By the long-continued
selection of such slight individual differences which occur in birds
kept in the same aviary, widely different races could certainly be
formed; and long-continued selection, important as is the result, does
nothing but preserve the variations which arise, as it appears to us,
spontaneously.
In these cases we see that domesticated animals vary in an indefinite
number of particulars, though treated as uniformly as is possible. On
the other hand, there are instances of animals and plants, which,
though they have been exposed to very different conditions, both under
nature and domestication, have varied in nearly the same manner. Mr.
Layard informs me that he has observed amongst the Caffres of South
Africa a dog singularly like an arctic Esquimaux dog. Pigeons in India
present nearly the same wide diversities of colour as in Europe; and I
have seen chequered and simply barred pigeons, and pigeons with blue
and white loins, from Sierra Leone, Madeira, England, and India. New
varieties of flowers are continually raised in different parts of Great
Britain, but many of these are found by the judges at our exhibitions
to be almost identical with old varieties. A vast number of new
fruit-trees and culinary vegetables have been produced in North
America: these differ from European varieties in the same general
manner as the several varieties raised in Europe differ from one
another; and no one has ever pretended that the climate of America has
given to the many American varieties any general character by which
they can be recognised. Nevertheless, from the facts previously
advanced on the authority of Mr. Meehan with respect to American and
European forest-trees it would be rash to affirm that varieties raised
in the two countries would not in the course of ages assume a
distinctive character. Dr. M. Masters has recorded a striking fact[58]
bearing on this subject: he raised numerous plants of _Hybiscus
syriacus_ from seed collected in South Carolina and the Holy Land,
where the parent-plants must have been exposed to considerably
different conditions; yet the seedlings from both localities broke into
two similar strains, one with obtuse leaves and purple or crimson
flowers, and the other with elongated leaves and more or less pink
flowers.
We may, also, infer the prepotent influence of the constitution of the
organism over the definite action of the conditions of life, from the
several cases given in the earlier chapters of parallel series of
varieties,—an important subject, hereafter to be more fully discussed.
Sub-varieties of the several kinds of wheat, gourds, peaches, and other
plants, and to a limited extent sub-varieties of the fowl, pigeon, and
dog, have been shown either to resemble or to differ from one another
in a closely corresponding or parallel manner. In other cases, a
variety of one species resembles a distinct species; or the varieties
of two distinct species resemble one another. Although these parallel
resemblances no doubt often result from reversion to the former
characters of a common progenitor; yet in other cases, when new
characters first appear, the resemblance must be attributed to the
inheritance of a similar constitution, and consequently to a tendency
to vary in the same manner. We see something of a similar kind in the
same monstrosity appearing and reappearing many times in the same
species of animal, and, as Dr. Maxwell Masters has remarked to me, in
the same species of plant.
We may at least conclude, that the amount of modification which animals
and plants have undergone under domestication does not correspond with
the degree to which they have been subjected to changed circumstances.
As we know the parentage of domesticated birds far better than of most
quadrupeds, we will glance through the list. The pigeon has varied in
Europe more than almost any other bird; yet it is a native species, and
has not been exposed to any extraordinary change of conditions. The
fowl has varied equally, or almost equally, with the pigeon, and is a
native of the hot jungles of India. Neither the peacock, a native of
the same country, nor the guinea-fowl, an inhabitant of the dry deserts
of Africa, has varied at all, or only in colour. The turkey, from
Mexico, has varied but little. The duck, on the other hand, a native of
Europe, has yielded some well-marked races; and as this is an aquatic
bird, it must have been subjected to a far more serious change in its
habits than the pigeon or even the fowl, which nevertheless have varied
in a much higher degree. The goose, a native of Europe and aquatic like
the duck, has varied less than any other domesticated bird, except the
peacock.
Bud-variation is, also, important under our present point of view, in
some few cases, as when all the eyes on the same tuber of the potato,
or all the fruit on the same plum-tree, or all the flowers on the same
plant, have suddenly varied in the same manner, it might be argued that
the variation had been definitely caused by some change in the
conditions to which the plants had been exposed; yet, in other cases,
such an admission is extremely difficult. As new characters sometimes
appear by bud-variation, which do not occur in the parent-species or in
any allied species, we may reject, at least in these cases, the idea
that they are due to reversion. Now it is well worth while to reflect
maturely on some striking case of bud-variation, for instance that of
the peach. This tree has been cultivated by the million in various
parts of the world, has been treated differently, grown on its own
roots and grafted on various stocks, planted as a standard, trained
against a wall, or under glass; yet each bud of each sub-variety keeps
true to its kind. But occasionally, at long intervals of time, a tree
in England, or under the widely different climate of Virginia, produces
a single bud, and this yields a branch which ever afterwards bears
nectarines. Nectarines differ, as every one knows, from peaches in
their smoothness, size, and flavour; and the difference is so great
that some botanists have maintained that they are specifically
distinct. So permanent are the characters thus suddenly acquired, that
a nectarine produced by bud-variation has propagated itself by seed. To
guard against the supposition that there is some fundamental
distinction between bud and seminal variation, it is well to bear in
mind that nectarines have likewise been produced from the stone of the
peach; and, reversely, peaches from the stone of the nectarine. Now is
it possible to conceive external conditions more closely alike than
those to which the buds on the same tree are exposed? Yet one bud
alone, out of the many thousands borne by the same tree, has suddenly,
without any apparent cause, produced a nectarine. But the case is even
stronger than this, for the same flower-bud has yielded a fruit,
one-half or one-quarter a nectarine, and the other half or
three-quarters a peach. Again, seven or eight varieties of the peach
have yielded by bud-variation nectarines: the nectarines thus produced,
no doubt, differ a little from one another; but still they are
nectarines. Of course there must be some cause, internal or external,
to excite the peach-bud to change its nature; but I cannot imagine a
class of facts better adapted to force on our minds the conviction that
what we call the external conditions of life are in many cases quite
insignificant in relation to any particular variation, in comparison
with the organisation or constitution of the being which varies.
It is known from the labours of Geoffroy Saint-Hilaire, and recently
from those of Dareste and others, that eggs of the fowl, if shaken,
placed upright, perforated, covered in part with varnish, etc., produce
monstrous chickens. Now these monstrosities may be said to be directly
caused by such unnatural conditions, but the modifications thus induced
are not of a definite nature. An excellent observer, M. Camille
Dareste,[59] remarks “that the various species of monstrosities are not
determined by specific causes; the external agencies which modify the
development of the embryo act solely in causing a perturbation—a
perversion in the normal course of development.” He compares the result
to what we see in illness: a sudden chill, for instance, affects one
individual alone out of many, causing either a cold, or sore-throat,
rheumatism, or inflammation of the lungs or pleura. Contagious matter
acts in an analogous manner.[60] We may take a still more specific
instance: seven pigeons were struck by rattle-snakes:[61] some suffered
from convulsions; some had their blood coagulated, in others it was
perfectly fluid; some showed ecchymosed spots on the heart, others on
the intestines, etc.; others again showed no visible lesion in any
organ. It is well known that excess in drinking causes different
diseases in different men; but in the tropics the effects of
intemperance differ from those caused in a cold climate;[62] and in
this case we see the definite influence of opposite conditions. The
foregoing facts apparently give us as good an idea as we are likely for
a long time to obtain, how in many cases external conditions act
directly, though not definitely, in causing modifications of structure.
_Summary._—There can be no doubt, from the facts given in this chapter,
that extremely slight changes in the conditions of life sometimes,
probably often, act in a definite manner on our domesticated
productions; and, as the action of changed conditions in causing
indefinite variability is accumulative, so it may be with their
definite action. Hence considerable and definite modifications of
structure probably follow from altered conditions acting during a long
series of generations. In some few instances a marked effect has been
produced quickly on all, or nearly all, the individuals which have been
exposed to a marked change of climate, food, or other circumstance.
This has occurred with European men in the United States, with European
dogs in India, with horses in the Falkland Islands, apparently with
various animals at Angora, with foreign oysters in the Mediterranean,
and with maize transported from one climate to another. We have seen
that the chemical compounds of some plants and the state of their
tissues are readily affected by changed conditions. A relation
apparently exists between certain characters and certain conditions, so
that if the latter be changed the character is lost—as with the colours
of flowers, the state of some culinary plants, the fruit of the melon,
the tail of fat-tailed sheep, and the peculiar fleeces of other sheep.
The production of galls, and the change of plumage in parrots when fed
on peculiar food or when inoculated by the poison of a toad, prove to
us what great and mysterious changes in structure and colour, may be
the definite result of chemical changes in the nutrient fluids or
tissues.
We now almost certainly know that organic beings in a state of nature
may be modified in various definite ways by the conditions to which
they have been long exposed, as in the case of the birds and other
animals in the northern and southern United States, and of American
trees in comparison with their representatives in Europe. But in many
cases it is most difficult to distinguish between the definite result
of changed conditions, and the accumulation through natural selection
of indefinite variations which have proved serviceable. If it profited
a plant to inhabit a humid instead of an arid station, a fitting change
in its constitution might possibly result from the direct action of the
environment, though we have no grounds for believing that variations of
the right kind would occur more frequently with plants inhabiting a
station a little more humid than usual, than with other plants. Whether
the station was unusually dry or humid, variations adapting the plant
in a slight degree for directly opposite habits of life would
occasionally arise, as we have good reason to believe from what we
actually see in other cases.
The organisation or constitution of the being which is acted on, is
generally a much more important element than the nature of the changed
conditions, in determining the nature of the variation. We have
evidence of this in the appearance of nearly similar modifications
under different conditions, and of different modifications under
apparently nearly the same conditions. We have still better evidence of
this in closely parallel varieties being frequently produced from
distinct races, or even distinct species; and in the frequent
recurrence of the same monstrosity in the same species. We have also
seen that the degree to which domesticated birds have varied, does not
stand in any close relation with the amount of change to which they
have been subjected.
To recur once again to bud-variations. When we reflect on the millions
of buds which many trees have produced, before some one bud has varied,
we are lost in wonder as to what the precise cause of each variation
can be. Let us recall the case given by Andrew Knight of the
forty-year-old tree of the yellow magnum bonum plum, an old variety
which has been propagated by grafts on various stocks for a very long
period throughout Europe and North America, and on which a single bud
suddenly produced the red magnum bonum. We should also bear in mind
that distinct varieties, and even distinct species,—as in the case of
peaches, nectarines, and apricots,—of certain roses and
camellias,—although separated by a vast number of generations from any
progenitor in common, and although cultivated under diversified
conditions, have yielded by bud-variation closely analogous varieties.
When we reflect on these facts we become deeply impressed with the
conviction that in such cases the nature of the variation depends but
little on the conditions to which the plant has been exposed, and not
in any especial manner on its individual character, but much more on
the inherited nature or constitution of the whole group of allied
beings to which the plant in question belongs. We are thus driven to
conclude that in most cases the conditions of life play a subordinate
part in causing any particular modification; like that which a spark
plays, when a mass of combustibles bursts into flame—the nature of the
flame depending on the combustible matter, and not on the spark.[63]
No doubt each slight variation must have its efficient cause; but it is
as hopeless an attempt to discover the cause of each, as to say why a
chill or a poison affects one man differently from another. Even with
modifications resulting from the definite action of the conditions of
life, when all or nearly all the individuals, which have been similarly
exposed, are similarly affected, we can rarely see the precise relation
between cause and effect. In the next chapter it will be shown that the
increased use or disuse of various organs produces an inherited effect.
It will further be seen that certain variations are bound together by
correlation as well as by other laws. Beyond this we cannot at present
explain either the causes or nature of the variability of organic
beings.
REFERENCES
[1] ‘Ueber den Einfluss der Isolirung auf die Artbildung,’ 1872.
[2] ‘Gardener’s Chronicle,’ 1853, p. 183.
[3] Mr. Wildman, ‘Floricultural Soc.,’ Feb. 7th, 1843, reported in
‘Gardener’s Chronicle,’ 1843, p. 86.
[4] Mr. Robson, in ‘Journal of Horticulture,’ Feb. 13th, 1866, p. 122.
[5] ‘Journal of Horticulture,’ 1861, p. 24.
[6] Ibid., 1862, p. 83.
[7] ‘Gardener’s Chronicle,’ 1845, p. 660.
[8] Ibid., 1863, p. 628.
[9] ‘Journal of Hort.,’ 1861, pp. 64, 309.
[10] ‘Des Variétés,’ etc., p. 76.
[11] Engel, ‘Sur les Prop. Médicales des Plantes,’ 1860, pp. 10, 25.
On changes in the odours of plants,_ see_ Dalibert’s Experiments
quoted by Beckman, ‘Inventions,’ vol. ii. p. 344; and Nees, in
Ferussac, ‘Bull. des Sc. Nat.,’ 1824, tom. i. p. 60. With respect to
the rhubarb, etc., _see also_ ‘Gardener’s Chronicle,’ 1849, p. 355;
1862, p. 1123.
[12] Hooker, ‘Flora Indica,’ p. 32.
[13] Naudin, ‘Annales des Sc. Nat.,’ 4th series, Bot., tom. xi., 1859,
p. 81. ‘Gardener’s Chronicle,’ 1859, p. 464.
[14] Moorcroft’s ‘Travels,’ etc., vol. ii. p. 143.
[15] ‘Gardener’s Chronicle,’ 1861, p. 1113.
[16] Royle, ‘Productive Resources of India,’ p. 59.
[17] ‘Personal Narrative,’ Eng. translat., vol. v. p. 101. This
statement has been confirmed by Karsten (‘Beitrag zur Kenntniss der
Rhynchoprion,’ Moscow, 1864, s. 39), and by others.
[18] ‘Organic Chemistry,’ Eng. translat., 1st edit., p. 369.
[19] Prichard, ‘Phys. Hist. of Mankind,’ 1851, vol. i. p. 155.
[20] Darwin, ‘Journal of Researches,’ 1845, p. 434.
[21] These statements on disease are taken from Dr. Boudin’s
‘Géographie et Statistique Médicale,’ 1857, tom. i. pp. xliv. and
lii.; tom. ii. p. 315.
[22] ‘Ceylon,’ by Sir J. E. Tennent, vol. i., 1859, p. 89.
[23] Godron, ‘De l’Espèce,’ tom. ii. p. 52.
[24] ‘Journal of Horticultural Soc.,’ vol. vii., 1852, p. 117.
[25] ‘Journal of Hort. Soc.,’ vol. i. p. 160.
[26] _See_ Lecoq, on the Villosity of Plants, ‘Géograph. Bot.,’ tom.
iii. pp. 287, 291; Gärtner, ‘Bastarderz.,’ s. 261; Mr. Masters on the
Opuntia, in ‘Gardener’s Chronicle,’ 1846, p. 444.
[27] ‘Pom. Phys.,’ p. 136.
[28] ‘Ampélographie,’ 1849, p. 19.
[29] Gärtner, ‘Bastarderz.,’ s. 606, has collected nearly all recorded
facts. Andrew Knight (in ‘Transact. Hort. Soc.,’ vol. ii. p. 160) goes
so far as to maintain that few varieties are absolutely permanent in
character when propagated by buds or grafts.
[30] Mr. Blyth, ‘Annals and Mag. of Nat. Hist.,’ vol. xx. 1847, p.
391.
[31] ‘Natural History Review,’ 1862, p. 113.
[32] ‘Journal of Roy. Geographical Soc.,’ vol. ix., 1839, p. 275.
[33] ‘Travels in Bokhara,’ vol. iii. p. 151.
[34] _See also,_ on the influence of marshy pastures on the wool,
Godron, ‘L’Espèce,’ tom. ii. p. 22.
[35] Isidore Geoffroy Saint-Hilaire, ‘Hist. Nat. Gén.,’ tom. iii. p.
438.
[36] Azara has made some good remarks on this subject, ‘Quadrupedes du
Paraguay,’ tom. ii. p. 337. _See_ an account of a family of naked mice
produced in England, ‘Proc. Zoolog. Soc.,’ 1856, p. 38.
[37] ‘Die Fauna der Pfahlbauten,’ 1861, s. 15.
[38] ‘Schweineschädel,’ 1864, s. 99.
[39] ‘Travels in Siberia,’ Eng. translat., vol. i. p. 228.
[40] A. R. Wallace, ‘Travels on the Amazon and Rio Negro,’ p. 294.
[41] ‘Naturgeschichte der Stubenvögel,’ 1840, s. 262, 308.
[42] ‘Hist. Nat Gén.,’ tom. iii. p. 402.
[43] ‘Bull. de La Soc. Imp. d’Acclimat.,’ tom. viii. p. 351.
[44] _See_ an account of Mr. Gregson’s experiments on the _ Abraxus
grossulariata,_ ‘Proc. Entomolog. Soc.,’ Jan. 6th, 1862: these
experiments have been confirmed by Mr. Greening, in ‘Proc. of the
Northern Entomolog. Soc.,’ July 28th, 1862. For the effects of food on
caterpillars, _see_ a curious account by M. Michely in ‘Bull. De La
Soc. Imp. d’Acclimat.,’ tom. viii. p. 563. For analogous facts from
Dahlbom on Hymenoptera, _see_ Westwood’s ‘Modern Class. of Insects,’
vol. ii. p. 98. _See also_ Dr. L. Moller ‘Die Abhängigkeit der
Insecten,’ 1867, s. 70.
[45] ‘The Principles of Biology,’ vol. ii., 1866. The present chapters
were written before I had read Mr. Herbert Spencer’s work, so that I
have not been able to make so much use of it as I should otherwise
probably have done.)
[46] Professor Weismann comes to the same conclusion with respect to
certain European butterflies in his valuable essay, ‘Ueber den
Saison-Dimorphismus,’ 1875. I might also refer to the recent works of
several other authors on the present subject; for instance to Kerner’s
‘Gute und schlechte Arten,’ 1866.
[47] ‘Proc. Acad. Nat. Soc. of Philadelphia,’ Jan. 28th, 1862.
[48] _See_ Mr. B. D. Walsh’s excellent papers in ‘Proc. Entomolog.
Soc. Philadelphia,’ Dec. 1866,, p. 284. With respect to the willow,
_see_ ibid., 1864. p. 546.
[49] See his admirable ‘Histoire des Galles’ in ‘Annal. des Sc. Nat.
Bot.’ 3rd series tom. 19 1853 p. 273.)
[50] Kirby and Spence’s ‘Entomology,’ 1818, vol. i. p. 450;
Lacaze-Duthiers, ibid., p. 284.
[51] ‘Proc. Entomolog. Soc. Philadelphia,’ 1864, p. 558.
[52] Mr. B. D. Walsh, ibid., p. 633, and Dec. 1866, p. 275.
[53] Mr. B. D. Walsh, ibid., 1864, pp. 545, 411, 495; and Dec. 1866,
p. 278. _See also_ Lacaze-Duthiers.
[54] Lacaze-Duthiers, ibid., pp. 325, 328.
[55] ‘Linnæa,’ vol. xvii. 1843; quoted by Dr. M. T. Masters, Royal
Institution, March 16th, 1860.
[56] ‘Proc. Acad. Nat. Sc., Philadelphia,’ June 16th, 1874, and July
23rd, 1875.
[57] Hewett C. Watson ‘Cybele Britannica,’ vol. i., 1847, p. 11.
[58] ‘Gardener’s Chronicle,’ 1857, p. 629.
[59] ‘Mémoire sur la Production Artificielle des Monstruosités,’ 1862,
pp. 8-12; ‘Recherches sur les Conditions, etc., chez les Monstres,’
1863, p. 6. An abstract is given of Geoffroy’s Experiments by his son,
in his ‘Vie, Travaux,’ etc., 1847, p. 290.
[60] Paget, ‘Lectures on Surgical Pathology,’ 1853, vol. i. p. 483.
[61] ‘Researches upon the Venom of the Rattle-snake,’ Jan. 1861, by
Dr. Mitchell, p. 67.
[62] Mr. Sedgwick, in ‘British and Foreign Medico-Chirurg. Review,’
July 1863, p. 175.
[63] Professor Weismann argues strongly in favour of this view in his
‘Saison-Dimorphismus der Schmetterlinge,’ 1875, pp. 40-43.