REPRODUCTION AND VARIATION.
BUD-VARIATION IN THE PEACH, PLUM, CHERRY, VINE, GOOSEBERRY, CURRANT,
AND BANANA, AS SHOWN BY THE MODIFIED FRUIT—IN FLOWERS: CAMELLIAS,
AZALEAS, CHRYSANTHEMUMS, ROSES, ETC—ON THE RUNNING OF THE COLOUR IN
CARNATIONS—BUD-VARIATIONS IN LEAVES—VARIATIONS BY SUCKERS, TUBERS, AND
BULBS—ON THE BREAKING OF TULIPS—BUD-VARIATIONS GRADUATE INTO CHANGES
CONSEQUENT ON CHANGED CONDITIONS OF LIFE—GRAFT-HYBRIDS—ON THE
SEGREGATION OF THE PARENTAL CHARACTERS IN SEMINAL HYBRIDS BY
BUD-VARIATION—ON THE DIRECT OR IMMEDIATE ACTION OF FOREIGN POLLEN ON
THE MOTHER-PLANT—ON THE EFFECTS IN FEMALE ANIMALS OF A PREVIOUS
IMPREGNATION ON THE SUBSEQUENT OFFSPRING—CONCLUSION AND SUMMARY
This chapter will be chiefly devoted to a subject in many respects
important, namely, bud-variation. By this term I include all those
sudden changes in structure or appearance which occasionally occur in
full-grown plants in their flower-buds or leaf-buds. Gardeners call
such changes “Sports;” but this, as previously remarked, is an
ill-defined expression, as it has often been applied to strongly marked
variations in seedling plants. The difference between seminal and bud
reproduction is not so great as it at first appears; for each bud is in
one sense a new and distinct individual; but such individuals are
produced through the formation of various kinds of buds without the aid
of any special apparatus, whilst fertile seeds are produced by the
concourse of the two sexual elements. The modifications which arise
through bud-variation can generally be propagated to any extent by
grafting, budding, cuttings, bulbs, etc., and occasionally even by
seed. Some few of our most beautiful and useful productions have arisen
by bud-variation.
Bud-variations have as yet been observed only in the vegetable kingdom;
but it is probable that if compound animals, such as corals, etc., had
been subjected to a long course of domestication, they would have
varied by buds; for they resemble plants in many respects. For
instance, any new or peculiar character presented by a compound animal
is propagated by budding, as occurs with differently coloured Hydras,
and as Mr. Gosse has shown to be the case with a singular variety of a
true coral. Varieties of the Hydra have also been grafted on other
varieties, and have retained their character.
I will in the first place give all the cases of bud variations which I
have been able to collect, and afterwards show their importance.[1]
These cases prove that those authors who, like Pallas, attribute all
variability to the crossing either of distinct races, or of distinct
individuals belonging to the same race but somewhat different from each
other, are in error; as are those authors who attribute all variability
to the mere act of sexual union. Nor can we account in all cases for
the appearance through bud-variation of new characters by the principle
of reversion to long-lost characters. He who wishes to judge how far
the conditions of life directly cause each particular variation ought
to reflect well on the cases immediately to be given. I will commence
with bud-variations, as exhibited in the fruit, and then pass on to
flowers, and finally to leaves.
_Peach (Amygdalus persica)._—In the last chapter I gave two cases of a
peach-almond and a double-flowered almond which suddenly produced fruit
closely resembling true peaches. I have also given many cases of
peach-trees producing buds, which, when developed into branches, have
yielded nectarines. We have seen that no less than six named and
several unnamed varieties of the peach have thus produced several
varieties of nectarine. I have shown that it is highly improbable that
all these peach-trees, some of which are old varieties, and have been
propagated by the million, are hybrids from the peach and nectarine,
and that it is opposed to all analogy to attribute the occasional
production of nectarines on peach-trees to the direct action of pollen
from some neighbouring nectarine-tree. Several of the cases are highly
remarkable, because, firstly, the fruit thus produced has sometimes
been in part a nectarine and in part a peach; secondly, because
nectarines thus suddenly produced have reproduced themselves by seed;
and thirdly, because nectarines are produced from peach-trees from seed
as well as from buds. The seed of the nectarine, on the other hand,
occasionally produces peaches; and we have seen in one instance that a
nectarine-tree yielded peaches by bud-variation. As the peach is
certainly the oldest or primary variety, the production of peaches from
nectarines, either by seeds or buds, may perhaps be considered as a
case of reversion. Certain trees have also been described as
indifferently bearing peaches or nectarines, and this may be considered
as bud-variation carried to an extreme degree.
The _grosse mignonne_ peach at Montreuil produced “from a sporting
branch” the _grosse mignonne tardive,_ “a most excellent variety,”
which ripens its fruit a fortnight later than the parent tree, and is
equally good.[2] This same peach has likewise produced by bud-variation
the _early grosse mignonne._ Hunt’s large tawny nectarine “originated
from Hunt’s small tawny nectarine, but not through seminal
reproduction.”[3]
_Plums._—Mr. Knight states that a tree of the yellow magnum bonum plum,
forty years old, which had always borne ordinary fruit, produced a
branch which yielded red magnum bonums.[4] Mr. Rivers, of
Sawbridgeworth, informs me (Jan. 1863) that a single tree out of 400 or
500 trees of the Early Prolific plum, which is a purple kind, descended
from an old French variety bearing purple fruit, produced when about
ten years old bright yellow plums; these differed in no respect except
colour from those on the other trees, but were unlike any other known
kind of yellow plum.[5]
_Cherry (Prunus cerasus)._—Mr. Knight has recorded (ibid.) the case of
a branch of a May-Duke cherry, which, though certainly never grafted,
always produced fruit, ripening later, and more oblong than the fruit
on the other branches. Another account has been given of two May-Duke
cherry-trees in Scotland, with branches bearing oblong and very fine
fruit, which invariably ripened, as in Knight’s case, a fortnight later
than the other cherries.[6] M. Carrière gives (p. 37) numerous
analogous cases, and one of the same tree bearing three kinds of fruit.
_Grapes (Vitis vinifera)._—The black or purple Frontignan in one case
produced during two successive years (and no doubt permanently), spurs
which bore white Frontignan grapes. In another case, on the same
footstalk, the lower berries “were well-coloured black Frontignans;
those next the stalk were white, with the exception of one black and
one streaked berry;” and altogether there were fifteen black and twelve
white berries on the same stalk. In another kind of grape, black and
amber-coloured berries were produced in the same cluster.[7] Count
Odart describes a variety which often bears on the same stalk small
round and large oblong berries; though the shape of the berry is
generally a fixed character.[8] Here is another striking case given on
the excellent authority of M. Carrière:[9] “a black Hamburg grape
(Frankenthal) was cut down, and produced three suckers; one of these
was layered, and after a time produced much smaller berries, which
always ripened at least a fortnight earlier than the others. Of the
remaining two suckers, one produced every year fine grapes, whilst the
other, although it set an abundance of fruit, matured only a few, and
these of inferior quality.”
_Gooseberry (Ribes grossularia)._—A remarkable case has been described
by Dr. Lindley[10] of a bush which bore at the same time no less than
four kinds of berries, namely, hairy and red,—smooth, small and
red,—green,—and yellow tinged with buff; the two latter kinds had a
different flavour from the red berries, and their seeds were coloured
red. Three twigs on this bush grew close together; the first bore three
yellow berries and one red; the second twig bore four yellow and one
red; and the third four red and one yellow. Mr. Laxton also informs me
that he has seen a Red Warrington gooseberry bearing both red and
yellow fruit on the same branch.
_Currant (Ribes rubrum)._—A bush purchased as the Champagne, which is a
variety that bears blush-coloured fruit intermediate between red and
white, produced during fourteen years on separate branches and mingled
on the same branch, berries of the red, white, and champagne kinds.[11]
The suspicion naturally arises that this variety may have originated
from a cross between a red and white variety, and that the above
transformation may be accounted for by reversion to both parent-forms;
but from the foregoing complex case of the gooseberry this view is
doubtful. In France, a branch of a red-currant bush, about ten years
old, produced near the summit five white berries) and lower down,
amongst the red berries, one berry half red and half white.[12]
Alexander Braun[13] also has often seen branches on white currant-trees
bearing red berries.
_Pear (Pyrus communis)._—Dureau de la Malle states that the flowers on
some trees of an ancient variety, the _doyenné galeux,_ were destroyed
by frost: other flowers appeared in July, which produced six pears;
these exactly resembled in their skin and taste the fruit of a distinct
variety, the _gros doyenne blanc,_ but in shape were like the
_bon-chrétien_: it was not ascertained whether this new variety could
be propagated by budding or grafting. The same author grafted a
_bon-chrétien_ on a quince, and it produced, besides its proper fruit,
an apparently new variety, of a peculiar form with thick and rough
skin.[14]
_Apple (Pyrus malus)._—In Canada, a tree of the variety called Pound
Sweet, produced,[15] between two of its proper fruit, an apple which
was well russeted, small in size, different in shape, and with a short
peduncle. As no russet apple grew anywhere near, this case apparently
cannot be accounted for by the direct action of foreign pollen. M.
Carrière (p. 38) mentions an analogous instance. I shall hereafter give
cases of apple-trees which regularly produce fruit of two kinds, or
half-and-half fruit; these trees are generally supposed, and probably
with truth, to be of crossed parentage, and that the fruit reverts to
both parent-forms.
_Banana (Musa sapientium)._—Sir R. Schomburgk states that he saw in St.
Domingo a raceme on the Fig Banana which bore towards the base 125
fruits of the proper kind; and these were succeeded, as is usual,
higher up the raceme, by barren flowers, and these by 420 fruits,
having a widely different appearance, and ripening earlier than the
proper fruit. The abnormal fruit closely resembled, except in being
smaller, that of the _Musa chinensis_ or _cavendishii,_ which has
generally been ranked as a distinct species.[16]
Flowers.—Many cases have been recorded of a whole plant, or single
branch, or bud, suddenly producing flowers different from the proper
type in colour, form, size, doubleness, or other character. Half the
flower, or a smaller segment, sometimes changes colour.
_Camellia._—The myrtle-leaved species (_C. myrtifolia_), and two or
three varieties of the common species, have been known to produce
hexagonal and imperfectly quadrangular flowers; and the branches
producing such flowers have been propagated by grafting.[17] The Pompon
variety often bears “four distinguishable kinds of flowers,—the pure
white and the red-eyed, which appear promiscuously; the brindled pink
and the rose-coloured, which may be kept separate with tolerable
certainty by grafting from the branches that bear them.” A branch,
also, on an old tree of the rose-coloured variety has been seen to
“revert to the pure white colour, an occurrence less common than the
departure from it.”[18]
_Cratægus oxyacantha._—A dark pink hawthorn has been known to throw out
a single tuft of pure white blossoms;[19] and Mr. A. Clapham,
nurseryman, of Bedford, informs me that his father had a deep crimson
thorn grafted on a white thorn, which during several years, always
bore, high above the graft, bunches of white, pink and deep crimson
flowers.
_Azalea indica_ is well known often to produce new varieties by buds. I
have myself seen several cases. A plant of _Azalea indica variegata_
has been exhibited bearing a truss of flowers of A. ind. gledstanesii
“as true as could possibly be produced, thus evidencing the origin of
that fine variety.” On another plant of _A. ind. variegata_ a perfect
flower of _A. ind. lateritia_ was produced; so that both _
gledstanesii_ and _lateritia_ no doubt originally appeared as sporting
branches of _A. ind. variegata._[20]
_Hibiscus (Paritium tricuspis)._—A seedling of this plant, when some
years old, produced, at Saharunpore,[21] some branches “which bore
leaves and flowers widely different from the normal form.” “The
abnormal leaf is much less divided, and not acuminated. The petals are
considerably larger, and quite entire. There is also in the fresh state
a conspicuous, large, oblong gland, full of a viscid secretion, on the
back of each of the calycine segments.” Dr. King, who subsequently had
charge of these Gardens, informs me that a tree of _Paritium tricuspis_
(probably the very same plant) growing there, had a branch buried in
the ground, apparently by accident; and this branch changed its
character wonderfully, growing like a bush, and producing flowers and
leaves, resembling in shape those of another species, viz., _ P.
tiliaceum._ A small branch springing from this bush near the ground,
reverted to the parent-form. Both forms were extensively propagated
during several years by cuttings and kept perfectly true.
_Althæa rosea._—A double yellow Hollyhock suddenly turned one year into
a pure white single kind; subsequently a branch bearing the original
double yellow flowers reappeared in the midst of the branches of the
single white kind.[22]
_Pelargonium._—These highly cultivated plants seem eminently liable to
bud-variation. I will give only a few well-marked cases. Gärtner has
seen[23] a plant of _P. zonale_ with a branch having white edges, which
remained constant for years, and bore flowers of a deeper red than
usual. Generally speaking, such branches present little or no
difference in their flowers: thus a writer[24] pinched off the leading
shoot of a seedling _P. zonale,_ and it threw out three branches, which
differed in the size and colour of their leaves and stems; but on all
three branches “the flowers were identical,” except in being largest in
the green-stemmed variety, and smallest in that with variegated
foliage: these three varieties were subsequently propagated and
distributed. Many branches, and some whole plants, of a variety called
_compactum,_ which bears orange-scarlet flowers, have been seen to
produce pink flowers.[25] Hill’s Hector, which is a pale red variety,
produced a branch with lilac flowers, and some trusses with both red
and lilac flowers. This apparently is a case of reversion, for Hill’s
Hector was a seedling from a lilac variety.[26] Here is a better case
of reversion: a variety produced from a complicated cross, after having
been propagated for five generations by seed, yielded by bud-variation
three very distinct varieties which were undistinguishable from plants,
“known to have been at some time ancestors of the plant in
question.”[27] Of all Pelargoniums, Rollisson’s Unique seems to be the
most sportive; its origin is not positively known, but is believed to
be from a cross. Mr. Salter, of Hammersmith, states[28] that he has
himself known this purple variety to produce the lilac, the
rose-crimson or _conspicuum,_ and the red or _coccineum_ varieties; the
latter has also produced the _rose d’amour_; so that altogether four
varieties have originated by bud variation from Rollisson’s Unique. Mr.
Salter remarks that these four varieties “may now be considered as
fixed, although they occasionally produce flowers of the original
colour. This year _ coccineum_ has pushed flowers of three different
colours, red, rose, and lilac, upon the same truss, and upon other
trusses are flowers half red and half lilac.” Besides these four
varieties, two other scarlet Uniques are known to exist, both of which
occasionally produce lilac flowers identical with Rollisson’s
Unique;[29] but one at least of these did not arise through
bud-variation, but is believed to be a seedling from Rollisson’s
Unique.[30] There are, also, in the trade[31] two other slightly
different varieties, of unknown origin, of Rollisson’s Unique: so that
altogether we have a curiously complex case of variation both by buds
and seeds.[32] Here is a still more complex case: M. Rafarin states
that a pale rose-coloured variety produced a branch bearing deep red
flowers. “Cuttings were taken from this ‘sport,’ from which 20 plants
were raised, which flowered in 1867, when it was found that scarcely
two were alike.” Some resembled the parent-form, some resembled the
sport, some bore both kinds of flowers; and even some of the petals on
the same flower were rose-coloured and others red.[33] An English wild
plant, the _Geranium pratense,_ when cultivated in a garden, has been
seen to produce on the same plant both blue and white, and striped blue
and white flowers.[34]
_Chrysanthemum._—This plant frequently sports, both by its lateral
branches and occasionally by suckers. A seedling raised by Mr. Salter
has produced by bud-variation six distinct sorts, five different in
colour and one in foliage, all of which are now fixed.[35] A variety
called _cedo nulli_ bears small yellow flowers, but habitually produces
branches with white flowers; and a specimen was exhibited, which Prof.
T. Dyer saw, before the Horticultural Society. The varieties which were
first introduced from China were so excessively variable, “that it was
extremely difficult to tell which was the original colour of the
variety, and which was the sport.” The same plant would produce one
year only buff-coloured, and next year only rose-coloured flowers; and
then would change again, or produce at the same time flowers of both
colours. These fluctuating varieties are now all lost, and, when a
branch sports into a new variety, it can generally be propagated and
kept true; but, as Mr. Salter remarks, “every sport should be
thoroughly tested in different soils before it can be really considered
as fixed, as many have been known to run back when planted in rich
compost; but when sufficient care and time are expended in proving,
there will exist little danger of subsequent disappointment.” Mr.
Salter informs me that with all the varieties the commonest kind of
bud-variation is the production of yellow flowers, and, as this is the
primordial colour, these cases may be attributed to reversion. Mr.
Salter has given me a list of seven differently coloured
chrysanthemums, which have all produced branches with yellow flowers;
but three of them have also sported into other colours. With any change
of colour in the flower, the foliage generally changes in a
corresponding manner in lightness or darkness.
Another Compositous plant, namely, Centauria cyanus, when cultivated in
a garden, not unfrequently produces on the same root flowers of four
different colours, viz., blue, white, dark-purple, and
parti-coloured.[36] The flowers of Anthemis also vary on the same
plant.[37]
_Roses._—Many varieties of the Rose are known or are believed to have
originated by bud-variation.[38] The common double moss-rose was
imported into England from Italy about the year 1735.[39] Its origin is
unknown, but from analogy it probably arose from the Provence rose (_R.
centifolia_) by bud-variation; for the branches of the common moss-rose
have several times been known to produce Provence roses, wholly or
partially destitute of moss: I have seen one such instance, and several
others have been recorded.[40] Mr. Rivers also informs me that he
raised two or three roses of the Provence class from seed of the old
single moss-rose;[41] and this latter kind was produced in 1807 by
bud-variation from the common moss-rose. The white moss-rose was also
produced in 1788 by an offset from the common red moss-rose: it was at
first pale blush-coloured, but became white by continued budding. On
cutting down the shoots which had produced this white moss-rose, two
weak shoots were thrown up, and buds from these yielded the beautiful
striped moss-rose. The common moss-rose has yielded by bud-variation,
besides the old single red moss-rose, the old scarlet semi-double
moss-rose, and the sage-leaf moss-rose, which “has a delicate
shell-like form, and is of a beautiful blush colour; it is now (1852)
nearly extinct.”[42] A white moss-rose has been seen to bear a flower
half white and half pink.[43] Although several moss-roses have thus
certainly arisen by bud-variation, the greater number probably owe
their origin to seed of moss-roses. For Mr. Rivers informs me that his
seedlings from the old single moss-rose almost always produced
moss-roses; and the old single moss-rose was, as we have seen, the
product by bud-variation of the double moss-rose originally imported
from Italy. That the original moss-rose was the product of
bud-variation is probable, from the facts above given and from the de
Meaux moss-rose (also a variety of _R. centifolia_)[44] having appeared
as a sporting branch on the common rose de Meaux. Prof. Caspary has
carefully described[45] the case of a six-year-old white moss-rose,
which sent up several suckers, one of which was thorny, and produced
red flowers, destitute of moss, exactly like those of the Provence rose
(_R. centifolia_): another shoot bore both kinds of flowers, and in
addition longitudinally striped flowers. As this white moss-rose had
been grafted on the Provence rose, Prof. Caspary attributes the above
changes to the influence of the stock; but from the facts already
given, and from others to be given, bud-variation, with reversion, is
probably a sufficient explanation.
Many other instances could be added of roses varying by buds. The white
Provence rose apparently originated in this way.[46] M. Carrière states
(p. 36) that he himself knows of five varieties thus produced by the
Baronne Prévost. The double and highly-coloured Belladonna rose has
produced by suckers both semi-double and almost single white roses;[47]
whilst suckers from one of these semi-double white roses reverted to
perfectly characterised Belladonnas. In St. Domingo, varieties of the
China rose propagated by cuttings often revert after a year or two into
the old China rose.[48] Many cases have been recorded of roses suddenly
becoming striped or changing their character by segments: some plants
of the Comtesse de Chabrillant, which is properly rose-coloured, were
exhibited in 1862,[49] with crimson flakes on a rose ground. I have
seen the Beauty of Billiard with a quarter and with half the flower
almost white. ‘The Austrian bramble _R. lutea_ not rarely[50] produces
branches with pure yellow flowers; and Prof. Henslow has seen exactly
half the flower of a pure yellow, and I have seen narrow yellow streaks
on a single petal, of which the rest was of the usual copper colour.
The following cases are highly remarkable. Mr. Rivers, as I am informed
by him, possessed a new French rose with delicate smooth shoots, pale
glaucous-green leaves, and semi-double pale flesh-coloured flowers
striped with dark red; and on branches thus characterised there
suddenly appeared in more than one instance, the famous old rose called
the Baronne Prevost, with its stout thorny shoots, and immense,
uniformly and richly coloured double flowers; so that in this case the
shoots, leaves, and flowers, all at once changed their character by
bud-variation. According to M. Verlot,[51] a variety called _Rosa
cannabifolia,_ which has peculiarly shaped leaflets, and differs from
every member of the family in the leaves being opposite instead of
alternate, suddenly appeared on a plant of _R. alba_ in the gardens of
the Luxembourg. Lastly, “a running shoot” was observed by Mr. H.
Curtis[52] on the old Aimée Vibert Noisette, and he budded it on
Celine; thus a climbing Aimée Vibert was first produced and afterwards
propagated.
_Dianthus._—It is quite common with the Sweet William (_D. barbatus_)
to see differently coloured flowers on the same root; and I have
observed on the same truss four differently coloured and shaded
flowers. Carnations and pinks (_D. caryophyllus,_ etc.) occasionally
vary by layers; and some kinds are so little certain in character that
they are called by floriculturists “catch-flowers.”[53] Mr. Dickson has
ably discussed the “running” of particoloured or striped carnations,
and says it cannot be accounted for by the compost in which they are
grown: “layers from the same clean flower would come part of them clean
and part foul, even when subjected to precisely the same treatment; and
frequently one flower alone appears influenced by the taint, the
remainder coming perfectly clean.”[54] This running of the
parti-coloured flowers apparently is a case of reversion by buds to the
original uniform tint of the species.
I will briefly mention some other cases of bud-variation to show how
many plants belonging to many orders have varied in their flowers; and
many others might be added. I have seen on a snap-dragon (_Antirrhinum
majus_) white, pink, and striped flowers on the same plant, and
branches with striped flowers on a red-coloured variety. On a double
stock (_Matthiola incana_) I have seen a branch bearing single flowers;
and on a dingy-purple double variety of the wall-flower (_Cheiranthus
cheiri_), a branch which had reverted to the ordinary copper colour. On
other branches of the same plant, some flowers were exactly divided
across the middle, one half being purple and the other coppery; but
some of the smaller petals towards the centre of these same flowers
were purple longitudinally streaked with coppery colour, or coppery
streaked with purple. A Cyclamen[55] has been observed to bear white
and pink flowers of two forms, the one resembling the Persicum strain,
and the other the Coum strain. _Oenothera biennis_ has been seen[56]
bearing flowers of three different colours. The hybrid _Gladiolus
colvilii_ occasionally bears uniformly coloured flowers, and one case
is recorded[57] of all the flowers on a plant thus changing colour. A
Fuchsia has been seen[58] bearing two kinds of flowers. _ Mirabilis
jalapa_ is eminently sportive, sometimes bearing on the same root pure
red, yellow, and white flowers, and others striped with various
combinations of these three colours.[59] The plants of the Mirabilis,
which bear such extraordinarily variable flowers in most, probably in
all, cases, owe their origin, as shown by Prof. Lecoq, to crosses
between differently coloured varieties.
_Leaves and Shoots._—Changes, through bud-variation, in fruits and
flowers have hitherto been treated of; incidentally some remarkable
modifications in the leaves and shoots of the rose and Paritium, and in
a lesser degree in the foliage of the Pelargonium and Chrysanthemum,
have been noticed. I will now add a few more cases of variation in
leaf-buds. Verlot[60] states that on _Aralia trifoliata,_ which
properly has leaves with three leaflets, branches frequently appear
bearing simple leaves of various forms; these can be propagated by buds
or by grafting, and have given rise, as he states, to several nominal
species.
With respect to trees, the history of but few of the many varieties
with curious or ornamental foliage is known; but several probably have
originated by bud-variation. Here is one case:—An old ash-tree
(_Fraxinus excelsior_) in the grounds of Necton, as Mr. Mason states,
“for many years has had one bough of a totally different character to
the rest of the tree, or of any other ash-tree which I have seen; being
short-jointed and densely covered with foliage.” It was ascertained
that this variety could be propagated by grafts.[61] The varieties of
some trees with cut leaves, as the oak-leaved laburnum, the
parsley-leaved vine, and especially the fern-leaved beech, are apt to
revert by buds to the common forms.[62] The fern-like leaves of the
beech sometimes revert only partially, and the branches display here
and there sprouts bearing common leaves, fern-like, and variously
shaped leaves. Such cases differ but little from the so-called
heterophyllus varieties, in which the tree habitually bears leaves of
various forms; but it is probable that most heterophyllous trees have
originated as seedlings. There is a sub-variety of the weeping willow
with leaves rolled up into a spiral coil; and Mr. Masters states that a
tree of this kind kept true in his garden for twenty-five years, and
then threw out a single upright shoot bearing flat leaves.[63]
I have often noticed single twigs and branches on beech and other trees
with their leaves fully expanded before those on the other branches had
opened; and as there was nothing in their exposure or character to
account for this difference, I presume that they had appeared as
bud-variations, like the early and late fruit-maturing varieties of the
peach and nectarine.
Cryptogamic plants are liable to bud-variation, for fronds on the same
fern often display remarkable deviations of structure. Spores, which
are of the nature of buds, taken from such abnormal fronds, reproduce,
with remarkable fidelity, the same variety, after passing through the
sexual stage.[64]
With respect to colour, leaves often become by bud-variation zoned,
blotched, or spotted with white, yellow, and red; and this occasionally
occurs even with plants in a state of nature. Variegation, however,
appears still more frequently in plants produced from seed; even the
cotyledons or seed-leaves being thus affected.[65] There have been
endless disputes whether variegation should be considered as a disease.
In a future chapter we shall see that it is much influenced, both in
the case of seedlings and of mature plants, by the nature of the soil.
Plants which have become variegated as seedlings, generally transmit
their character by seed to a large proportion of their progeny; and Mr.
Salter has given me a list of eight genera in which this occurred.[66]
Sir F. Pollock has given me more precise information: he sowed seed
from a variegated plant of _Ballota nigra_ which was found growing
wild, and thirty per cent of the seedlings were variegated; seed from
these latter being sown, sixty per cent came up variegated. When
branches become variegated by bud-variation, and the variety is
attempted to be propagated by seed, the seedlings are rarely
variegated: Mr. Salter found this to be the case with plants belonging
to eleven genera, in which the greater number of the seedlings proved
to be green-leaved; yet a few were slightly variegated, or were quite
white, but none were worth keeping. Variegated plants, whether
originally produced from seeds or buds, can generally be propagated by
budding, grafting, etc.; but all are apt to revert by bud-variation to
their ordinary foliage. This tendency, however, differs much in the
varieties of even the same species; for instance, the golden-striped
variety of _Euonymus japonicus_ “is very liable to run back to the
green-leaved, while the silver-striped variety hardly ever
changes.”[67] I have seen a variety of the holly, with its leaves
having a central yellow patch, which had everywhere partially reverted
to the ordinary foliage, so that on the same small branch there were
many twigs of both kinds. In the pelargonium, and in some other plants,
variegation is generally accompanied by some degree of dwarfing, as is
well exemplified in the “Dandy” pelargonium. When such dwarf varieties
sport back by buds or suckers to the ordinary foliage, the dwarfed
stature still remains.[68] It is remarkable that plants propagated from
branches which have reverted from variegated to plain leaves[69] do not
always (or never, as one observer asserts) perfectly resemble the
original plain-leaved plant from which the variegated branch arose: it
seems that a plant, in passing by bud-variation from plain leaves to
variegated, and back again from variegated to plain, is generally in
some degree affected so as to assume a slightly different aspect.
_Bud-variation by Suckers, Tubers, and Bulbs._—All the cases hitherto
given of bud-variation in fruits, flowers, leaves, and shoots, have
been confined to buds on the stems or branches, with the exception of a
few cases incidentally noticed of varying suckers in the rose,
pelargonium, and chrysanthemum. I will now give a few instances of
variation in subterranean buds, that is, by suckers, tubers, and bulbs;
not that there is any essential difference between buds above and
beneath the ground. Mr. Salter informs me that two variegated varieties
of Phlox originated as suckers; but I should not have thought these
worth mentioning, had not Mr. Salter found, after repeated trials, that
he could not propagate them by “root-joints,” whereas, the variegated
_Tussilago farfara_ can thus be safely propagated;[70] but this latter
plant may have originated as a variegated seedling, which would account
for its greater fixedness of character. The Barberry (_Berberis
vulgaris_) offers an analogous case; there is a well-known variety with
seedless fruit, which can be propagated by cuttings or layers; but
suckers always revert to the common form, which produces fruit
containing seeds.[71] My father repeatedly tried this experiment, and
always with the same result. I may here mention that maize and wheat
sometimes produce new varieties from the stock or root, as does the
sugar-cane.[72]
Turning now to tubers: in the common Potato (_Solanum tuberosum_) a
single bud or eye sometimes varies and produces a new variety; or,
occasionally, and this is a much more remarkable circumstance, all the
eyes in a tuber vary in the same manner and at the same time, so that
the whole tuber assumes a new character. For instance, a single eye in
a tuber of the old _Forty-fold potato,_ which is a purple variety, was
observed[73] to become white; this eye was cut out and planted
separately, and the kind has since been largely propagated. _Kemp’s
potato_ is properly white, but a plant in Lancashire produced two
tubers which were red, and two which were white; the red kind was
propagated in the usual manner by eyes, and kept true to its new
colour, and, being found a more productive variety, soon became widely
known under the name of _ Taylor’s forty-fold._[74] The old _Forty-fold
potato,_ as already stated, is a purple variety; but a plant long
cultivated on the same ground produced, not, as in the case above
given, a single white eye, but a whole white tuber, which has since
been propagated and keeps true.[75] Several cases have been recorded of
large portions of whole rows of potatoes slightly changing their
character.[76]
Dahlias propagated by tubers under the hot climate of St. Domingo vary
much; Sir R. Schomburgk gives the case of the “Butterfly variety,”
which the second year produced on the same plant “double and single
flowers; here white petals edged with maroon; there of a uniform deep
maroon.”[77] Mr. Bree also mentions a plant “which bore two different
kinds of self-coloured flowers, as well as a third kind which partook
of both colours beautifully intermixed.”[78] Another case is described
of a dahlia with purple flowers which bore a white flower streaked with
purple.[79]
Considering how long and extensively many Bulbous plants have been
cultivated, and how numerous are the varieties produced from seed,
these plants have not perhaps varied so much by offsets,—that is, by
the production of new bulbs,—as might have been expected. With the
Hyacinth, however, several instances have been given by M. Carrière. A
case also has been recorded of a blue variety which for three
successive years gave offsets producing white flowers with a red
centre.[80] Another hyacinth bore[81] on the same truss a perfectly
pink and a perfectly blue flower. I have seen a bulb producing at the
same time one stalk or truss with fine blue flowers, another with fine
red flowers, and a third with blue flowers on one side and red on the
other; several of the flowers being also longitudinally striped red and
blue.
Mr. John Scott informs me that in 1862 _Imatophyllum miniatum,_ in the
Botanic Gardens of Edinburgh, threw up a sucker which differed from the
normal form, in the leaves being two-ranked instead of four-ranked. The
leaves were also smaller, with the upper surface raised instead of
being channelled.
In the propagation of _Tulips,_ seedlings are raised, called _selfs_ or
_breeders,_ which, “consist of one plain colour on a white or yellow
bottom. These, being cultivated on a dry and rather poor soil, become
broken or variegated and produce new varieties. The time that elapses
before they break varies from one to twenty years or more, and
sometimes this change never takes place.”[82] The broken or variegated
colours which give value to all tulips are due to bud-variation; for
although the Bybloemens and some other kinds have been raised from
several distinct breeders, yet all the Baguets are said to have come
from a single breeder or seedling. This bud-variation, in accordance
with the views of MM. Vilmorin and Verlot,[83] is probably an attempt
to revert to that uniform colour which is natural to the species. A
tulip, however, which has already become broken, when treated with too
strong manure, is liable to flush or lose by a second act of reversion
its variegated colours. Some kinds, as Imperatrix Florum, are much more
liable than others to flushing; and Mr. Dickson maintains[84] that this
can no more be accounted for than the variation of any other plant. He
believes that English growers, from care in choosing seed from broken
flowers instead of from plain flowers, have to a certain extent
diminished the tendency in flowers already broken to flushing or
secondary reversion. _Iris xiphium,_ according to M. Carrière (p. 65),
behaves in nearly the same manner, as do so many tulips.
During two consecutive years all the early flowers in a bed of
_Tigridia conchiflora_[85] resembled those of the old _T. pavonia_; but
the later flowers assumed their proper colour of fine yellow, spotted
with crimson. An apparently authentic account has been published[86] of
two forms of Hemerocallis, which have been universally considered as
distinct species, changing into each other; for the roots of the
large-flowered tawny _H. fulva,_ being divided and planted in a
different soil and place, produced the small-flowered _H. flava,_ as
well as some intermediate forms. It is doubtful whether such cases as
these latter, as well as the “flushing” of broken tulips and the
“running” of particoloured carnations,—that is, their more or less
complete return to a uniform tint,—ought to be classed under
bud-variation, or ought to be retained for the chapter in which I treat
of the direct action of the conditions of life on organic beings. These
cases, however, have this much in bud-variation, that the change is
effected through buds and not through seminal reproduction. But, on the
other hand, there is this difference—that in ordinary cases of
bud-variation, one bud alone changes, whilst in the foregoing cases all
the buds on the same plant were modified together. With the potato, we
have seen an intermediate case, for all the eyes in one tuber
simultaneously changed their character.
I will conclude with a few allied cases, which may be ranked either
under bud-variation, or under the direct action of the conditions of
life. When the common Hepatica is transplanted from its native woods,
the flowers change colour, even during the first year.[87] It is
notorious that the improved varieties of the Heartsease (_Viola
tricolor_), when transplanted, often produce flowers widely different
in size, form, and colour: for instance, I transplanted a large
uniformly-coloured dark purple variety, whilst in full flower, and it
then produced much smaller, more elongated flowers, with the lower
petals yellow; these were succeeded by flowers marked with large purple
spots, and ultimately, towards the end of the same summer, by the
original large dark purple flowers. The slight changes which some
fruit-trees undergo from being grafted and regrafted on various
stocks,[88] were considered by Andrew Knight[89] as closely allied to
“sporting branches,” or bud-variations. Again, we have the case of
young fruit-trees changing their character as they grow old; seedling
pears, for instance, lose with age their spines and improve in the
flavour of their fruit. Weeping birch-trees, when grafted on the common
variety, do not acquire a perfect pendulous habit until they grow old:
on the other hand, I shall hereafter give the case of some weeping
ashes which slowly and gradually assumed an upright habit of growth.
All such changes, dependent on age, may be compared with the changes,
alluded to in the last chapter, which many trees naturally undergo; as
in the case of the Deodar and Cedar of Lebanon, which are unlike in
youth, whilst they closely resemble each other in old age; and as with
certain oaks, and with some varieties of the lime and hawthorn.[90]
_Graft-hybrids._—Before giving a summary on Bud-variation I will
discuss some singular and anomalous cases, which are more or less
closely related to this same subject. I will begin with the famous case
of Adam’s laburnum or _Cytisus adami,_ a form or hybrid intermediate
between two very distinct species, namely, _C. laburnum_ and
_purpureus,_ the common and purple laburnum; but as this tree has often
been described, I will be as brief as I can.
Throughout Europe, in different soils and under different climates,
branches on this tree have repeatedly and suddenly reverted to the two
parent species in their flowers and leaves. To behold mingled on the
same tree tufts of dingy-red, bright yellow, and purple flowers, borne
on branches having widely different leaves and manner of growth, is a
surprising sight. The same raceme sometimes bears two kinds of flowers;
and I have seen a single flower exactly divided into halves, one side
being bright yellow and the other purple; so that one half of the
standard-petal was yellow and of larger size, and the other half purple
and smaller. In another flower the whole corolla was bright yellow, but
exactly half the calyx was purple. In another, one of the dingy-red
wing-petals had a narrow bright yellow stripe on it; and lastly, in
another flower, one of the stamens, which had become slightly
foliaceous, was half yellow and half purple; so that the tendency to
segregation of character or reversion affects even single parts and
organs.[91] The most remarkable fact about this tree is that in its
intermediate state, even when growing near both parent-species, it is
quite sterile; but when the flowers become pure yellow or pure purple
they yield seed. I believe that the pods from the yellow flowers yield
a full complement of seed; they certainly yield a larger number. Two
seedlings raised by Mr. Herbert from such seed[92] exhibited a purple
tinge on the stalks of their flowers; but several seedlings raised by
myself resembled in every character the common laburnum, with the
exception that some of them had remarkably long racemes: these
seedlings were perfectly fertile. That such purity of character and
fertility should be suddenly reacquired from so hybridised and sterile
a form is an astonishing phenomenon. The branches with purple flowers
appear at first sight exactly to resemble those of _C. purpureus_; but
on careful comparison I found that they differed from the pure species
in the shoots being thicker, the leaves a little broader, and the
flowers slightly shorter, with the corolla and calyx less brightly
purple: the basal part of the standard-petal also plainly showed a
trace of the yellow stain. So that the flowers, at least in this
instance, had not perfectly recovered their true character; and in
accordance with this, they were not perfectly fertile, for many of the
pods contained no seed, some produced one, and very few contained as
many as two seeds; whilst numerous pods on a tree of the pure _C.
purpureus_ in my garden contained three, four, and five fine seeds. The
pollen, moreover, was very imperfect, a multitude of grains being small
and shrivelled; and this is a singular fact; for, as we shall
immediately see, the pollen-grains in the dingy-red and sterile flowers
on the parent-tree, were, in external appearance, in a much better
state, and included very few shrivelled grains. Although the pollen of
the reverted purple flowers was in so poor a condition, the ovules were
well formed, and the seeds, when mature, germinated freely with me. Mr.
Herbert raised plants from seeds of the reverted purple flowers, and
they differed a _very little_ from the usual state of _C. purpureus._
Some which I raised in the same manner did not differ at all, either in
the character of their flowers or of the whole bush, from the pure _C.
purpureus._
Prof. Caspary has examined the ovules of the dingy-red and sterile
flowers in several plants of _C. adami_ on the Continent,[93] and finds
them generally monstrous. In three plants examined by me in England,
the ovules were likewise monstrous, the nucleus varying much in shape,
and projecting irregularly beyond the proper coats. The pollen grains,
on the other hand, judging from their external appearance, were
remarkably good, and readily protruded their tubes. By repeatedly
counting, under the microscope, the proportional number of bad grains,
Prof. Caspary ascertained that only 2·5 per cent were bad, which is a
less proportion than in the pollen of three pure species of Cytisus in
their cultivated state, viz., _C. purpureus, laburnum,_ and _alpinus._
Although the pollen of _C. adami_ is thus in appearance good, it does
not follow, according to M. Naudin’s observation[94] on Mirabilis, that
it would be functionally effective. The fact of the ovules of _C.
adami_ being monstrous, and the pollen apparently sound, is all the
more remarkable, because it is opposed to what usually occurs not only
with most hybrids,[95] but with two hybrids in the same genus, namely
in _C. purpureo-elongatus,_ and _C. alpino-laburnum._ In both these
hybrids, the ovules, as observed by Prof. Caspary and myself, were
well-formed, whilst many of the pollen-grains were ill-formed; in the
latter hybrid 20.3 per cent, and in the former no less than 84·8 per
cent of the grains were ascertained by Prof. Caspary to be bad. This
unusual condition of the male and female reproductive elements in _C.
adami_ has been used by Prof. Caspary as an argument against this plant
being considered as an ordinary hybrid produced from seed; but we
should remember that with hybrids the ovules have not been examined
nearly so frequently as the pollen, and they may be much oftener
imperfect than is generally supposed. Dr. E. Bornet, of Antibes,
informs me (through Mr. J. Traherne Moggridge) that with hybrid Cisti
the ovarium is frequently deformed, the ovules being in some cases
quite absent, and in other cases incapable of fertilisation.
Several theories have been propounded to account for the origin of _C.
adami,_ and for the transformations which it undergoes. The whole case
has been attributed by some authors to bud-variation; but considering
the wide difference between _C. laburnum_ and _purpureus,_ both of
which are natural species, and considering the sterility of the
intermediate form, this view may be summarily rejected. We shall
presently see that, with hybrid plants, two embryos differing in their
characters may be developed within the same seed and cohere; and it has
been supposed that _C. adami_ thus originated. Many botanists maintain
that _C. adami_ is a hybrid produced in the common way by seed, and
that it has reverted by buds to its two parent-forms. Negative results
are not of much value; but Reisseck, Caspary, and myself, tried in vain
to cross _C. laburnum_ and _purpureus_; when I fertilised the former
with pollen of the latter, I had the nearest approach to success, for
pods were formed, but in sixteen days after the withering of the
flowers, they fell off. Nevertheless, the belief that _C. adami_ is a
spontaneously produced hybrid between these two species is supported by
the fact that such hybrids have arisen in this genus. In a bed of
seedlings from _C. elongatus,_ which grew near to _C. purpureus,_ and
was probably fertilised by it through the agency of insects (for these,
as I know by experiment, play an important part in the fertilisation of
the laburnum), the sterile hybrid _C. purpureo-elongatus_ appeared.[96]
Thus, also, Waterer’s laburnum, the _C. alpino-laburnum,_[97]
spontaneously appeared, as I am informed by Mr. Waterer, in a bed of
seedlings.
On the other hand, we have a clear and distinct account given to
Poiteau,[98] by M. Adam, who raised the plant, showing that _C. adami_
is not an ordinary hybrid; but is what may be called a graft-hybrid,
that is, one produced from the united cellular tissue of two distinct
species. M. Adam inserted in the usual manner a shield of the bark of
_C. purpureus_ into a stock of _C. laburnum_; and the bud lay dormant,
as often happens, for a year; the shield then produced many buds and
shoots, one of which grew more upright and vigorous with larger leaves
than the shoots of _C. purpureus,_ and was consequently propagated. Now
it deserves especial notice that these plants were sold by M. Adam, as
a variety of _C. purpureus,_ before they had flowered; and the account
was published by Poiteau after the plants had flowered, but before they
had exhibited their remarkable tendency to revert into the two parent
species. So that there was no conceivable motive for falsification, and
it is difficult to see how there could have been any error.[99] If we
admit as true M. Adam’s account, we must admit the extraordinary fact
that two distinct species can unite by their cellular tissue, and
subsequently produce a plant bearing leaves and sterile flowers
intermediate in character between the scion and stock, and producing
buds liable to reversion; in short, resembling in every important
respect a hybrid formed in the ordinary way by seminal reproduction.
I will therefore give all the facts which I have been able to collect
on the formation of hybrids between distinct species or varieties,
without the intervention of the sexual organs. For if, as I am now
convinced, this is possible, it is a most important fact, which will
sooner or later change the views held by physiologists with respect to
sexual reproduction. A sufficient body of facts will afterwards be
adduced, showing that the segregation or separation of the characters
of the two parent-forms by bud-variation, as in the case of _Cytisus
adami,_ is not an unusual though a striking phenomenon. We shall
further see that a whole bud may thus revert, or only half, or some
smaller segment.
The famous _bizzarria Orange_ offers a strictly parallel case to that
of _Cytisus adami._ The gardener who in 1644 in Florence raised this
tree, declared that it was a seedling which had been grafted; and after
the graft had perished, the stock sprouted and produced the bizzarria.
Gallesio, who carefully examined several living specimens and compared
them with the description given by the original describer, P.
Nato,[100] states that the tree produces at the same time leaves,
flowers, and fruit identical with the bitter orange and with the citron
of Florence, and likewise compound fruit, with the two kinds either
blended together, both externally and internally, or segregated in
various ways. This tree can be propagated by cuttings, and retains its
diversified character. The so-called trifacial orange of Alexandria and
Smyrna[101] resembles in its general nature the bizzarria, and differs
only in the orange being of the sweet kind; this and the citron are
blended together in the same fruit, or are separately produced on the
same tree; nothing is known of its origin. In regard to the bizzarria,
many authors believe that it is a graft-hybrid; Gallesio, on the other
hand, thinks that it is an ordinary hybrid, with the habit of partially
reverting by buds to the two parent-forms; and we have seen that the
species in this genus often cross spontaneously.
It is notorious that when the variegated Jessamine is budded on the
common kind, the stock sometimes produces buds bearing variegated
leaves: Mr. Rivers, as he informs me, has seen instances of this. The
same thing occurs with the Oleander.[102] Mr. Rivers, on the authority
of a trustworthy friend, states that some buds of a golden-variegated
ash, which were inserted into common ashes, all died except one; but
the ash-stocks were affected,[103] and produced, both above and below
the points of insertion of the plates of bark bearing the dead buds,
shoots which bore variegated leaves. Mr. J. Anderson Henry has
communicated to me a nearly similar case: Mr. Brown, of Perth, observed
many years ago, in a Highland glen, an ash-tree with yellow leaves; and
buds taken from this tree were inserted into common ashes, which in
consequence were affected, and produced the _Blotched Breadalbane Ash._
This variety has been propagated, and has preserved its character
during the last fifty years. Weeping ashes, also, were budded on the
affected stocks, and became similarly variegated. It has been
repeatedly proved that several species of Abutilon, on which the
variegated _A. thompsonii_ has been grafted, become variegated.[104]
Many authors consider variegation as the result of disease; and the
foregoing cases may be looked at as the direct result of the
inoculation of a disease or some weakness. This has been almost proved
to be the case by Morren in the excellent paper just referred to, who
shows that even a leaf inserted by its footstalk into the bark of the
stock is sufficient to communicate variegation to it, though the leaf
soon perishes. Even fully formed leaves on the stock of Abutilon are
sometimes affected by the graft and become variegated. Variegation is
much influenced, as we shall hereafter see, by the nature of the soil
in which the plants are grown; and it does not seem improbable that
whatever change in the sap or tissues certain soils induce, whether or
not called a disease, might spread from the inserted piece of bark to
the stock. But a change of this kind cannot be considered to be of the
nature of a graft-hybrid.
There is a variety of the hazel with dark-purple leaves, like those of
the copper-beech: no one has attributed this colour to disease, and it
apparently is only an exaggeration of a tint which may often be seen on
the leaves of the common hazel. When this variety is grafted on the
common hazel,[105] it sometimes colours, as has been asserted, the
leaves below the graft; although negative evidence is not of much
value, I may add that Mr. Rivers, who has possessed hundreds of such
grafted trees, has never seen an instance.
Gärtner[106] quotes two separate accounts of branches of dark and
white-fruited vines which had been united in various ways, such as
being split longitudinally, and then joined, etc.; and these branches
produced distinct bunches of grapes of the two colours, and other
bunches with berries, either striped, or of an intermediate and new
tint. Even the leaves in one case were variegated. These facts are the
more remarkable because Andrew Knight never succeeded in raising
variegated grapes by fertilising white kinds by pollen of dark kinds;
though, as we have seen, he obtained seedlings with variegated fruits
and leaves, by fertilising a white variety by the already variegated
dark Aleppo grape. Gärtner attributes the above-quoted cases merely to
bud-variation; but it is a strange coincidence that the branches which
had been grafted in a peculiar manner should alone thus have varied;
and H. Adorne de Tscharner positively asserts that he produced the
described result more than once, and could do so at will, by splitting
and uniting the branches in the manner described by him.
I should not have quoted the following case had not the author of ‘Des
Jacinthes’[107] impressed me with the belief not only of his extensive
knowledge, but of his truthfulness: he says that bulbs of blue and red
hyacinths may be cut in two, and that they will grow together and throw
up a united stem (and this I have myself seen) with flowers of the two
colours on the opposite sides. But the remarkable point is, that
flowers are sometimes produced with the two colours blended together,
which makes the case closely analogous with that of the blended colours
of the grapes on the united vine branches.
In the case of roses it is supposed that several graft-hybrids have
been formed, but there is much doubt about these cases, owing to the
frequency of ordinary bud-variations. The most trustworthy instance
known to me is one, recorded by Mr. Poynter,[108] who assures me in a
letter of the entire accuracy of the statement. _ Rosa devoniensis_ had
been budded some years previously on a white Banksian rose; and from
the much enlarged point of junction, whence the Devoniensis and
Banksian still continued to grow, a third branch issued, which was
neither pure Banksian nor pure Devoniensis, but partook of the
character of both; the flowers resembled, but were superior in
character to those of the variety called _Lamarque_ (one of the
Noisettes), while the shoots were similar in their manner of growth to
those of the Banksian rose, with the exception that the longer and more
robust shoots were furnished with prickles. This rose was exhibited
before the Floral Committee of the Horticultural Society of London. Dr.
Lindley examined it and concluded that it had certainly been produced
by the mingling of _R. banksiæ_ with some rose like _R. devoniensis,_
“for while it was very greatly increased in vigour and in size of all
the parts, the leaves were half-way between a Banksian and Tea-scented
rose.” It appears that rose-growers were previously aware that the
Banksian rose sometimes affects other roses. As Mr. Poynter’s new
variety is intermediate in its fruit and foliage between the stock and
scion, and as it arose from the point of junction between the two, it
is very improbable that it owes its origin to mere bud-variation,
independently of the mutual influence of the stock and scion.
Lastly, with respect to potatoes. Mr. R. Trail stated in 1867 before
the Botanical Society of Edinburgh (and has since given me fuller
information), that several years ago he cut about sixty blue and white
potatoes into halves through the eyes or buds, and then carefully
joined them, destroying at the same time the other eyes. Some of these
united tubers produced white, and others blue tubers; some, however,
produced tubers partly white and partly blue; and the tubers from about
four or five were regularly mottled with the two colours. In these
latter cases we may conclude that a stem had been formed by the union
of the bisected buds, that is, by graft-hybridisation.
In the ‘Botanische Zeitung’ (May 16, 1868), Professor Hildebrand gives
an account with a coloured figure, of his experiments on two varieties
which were found during the same season to be constant in character,
namely, a somewhat elongated rough-skinned red potato and a rounded
smooth white one. He inserted buds reciprocally into both kinds,
destroying the other buds. He thus raised two plants, and each of these
produced a tuber intermediate in character between the two
parent-forms. That from the red bud grafted into the white tuber, was
at one end red and rough, as the whole tuber ought to have been if not
affected; in the middle it was smooth with red stripes, and at the
other end smooth and altogether white like that of the stock.
Mr. Taylor, who had received several accounts of potatoes having been
grafted by wedge-shaped pieces of one variety inserted into another,
though sceptical on the subject, made twenty-four experiments which he
described in detail before the Horticultural Society.[109] He thus
raised many new varieties, some like the graft or like the stock;
others having an intermediate character. Several persons witnessed the
digging up of the tubers from these graft-hybrids; and one of them, Mr.
Jameson, a large dealer in potatoes, writes thus, “They were such a
mixed lot, as I have never before or since seen. They were of all
colours and shapes, some very ugly and some very handsome.” Another
witness says “some were round, some kidney, pink-eyed kidney, piebald,
and mottled red and purple, of all shapes and sizes.” Some of these
varieties have been found valuable, and have been extensively
propagated. Mr. Jameson took away a large piebald potato which he cut
into five sets and propagated; these yielded round, white, red, and
piebald potatoes.
Mr. Fitzpatrick followed a different plan;[110] he grafted together not
the tubers but the young stems of varieties producing black, white, and
red potatoes. The tubers borne by three of these twin or united plants
were coloured in an extraordinary manner; one was almost exactly half
black and half white, so that some persons on seeing it thought that
two potatoes had been divided and rejoined; other tubers were half red
and half white, or curiously mottled with red and white, or with red
and black, according to the colours of the graft and stock.
The testimony of Mr. Fenn is of much value, as he is “a well known
potato-grower” who has raised many new varieties by crossing different
kinds in the ordinary manner. He considers it “demonstrated” that new,
intermediate varieties can be produced by grafting the tubers, though
he doubts whether such will prove valuable.[111] He made many trials
and laid the results, exhibiting specimens, before the Horticultural
Society. Not only were the tubers affected, some being smooth and white
at one end and rough and red at the other, but the stems and leaves
were modified in their manner of growth, colour and precocity. Some of
these graft-hybrids after being propagated for three years still showed
in their haulms their new character, different from that of the kind
from which the eyes had been taken. Mr. Fenn gave twelve of the tubers
of the third generation to Mr. Alex. Dean, who grew them, and was thus
converted into a believer in graft-hybridisation, having previously
been a complete sceptic. For comparison he planted the pure
parent-forms alongside the twelve tubers; and found that many of the
plants from the latter[112] were intermediate between the two
parent-forms in precocity, in the tallness, uprightness, jointing, and
robustness of the stems, and in the size and colour of the leaves.
Another experimentalist, Mr. Rintoul, grafted no less than fifty-nine
tubers, which differed in shape (some being kidneys) in smoothness and
colour,[113] and many of the plants thus raised “were intermediate in
the tubers as well as in the haulms.” He describes the more striking
cases.
In 1871 I received a letter from Mr. Merrick, of Boston, U.S.A., who
states that, “Mr. Fearing Burr, a very careful experimenter and author
of a much valued book, ‘The Garden Vegetables of America’ has succeeded
in producing distinctly mottled and most curious potatoes—evidently
graft-hybrids, by inserting eyes from blue or red potatoes into the
substance of white ones, after removing the eyes of the latter. I have
seen the potatoes, and they are very curious.”
We will now turn to the experiments made in Germany, since the
publication of Prof. Hildebrand’s paper. Herr Magnus relates[114] the
results of numerous trials made by Herren Reuter and Lindemuth, both
attached to the Royal Gardens of Berlin. They inserted the eyes of red
potatoes into white ones, and _vice versa._ Many different forms
partaking of the characters of the inserted bud and of the stock were
thus obtained; for instance, some of the tubers were white with red
eyes.
Herr Magnus also exhibited in the following year before the same
Society (Nov. 19, 1872), the produce of grafts between black, white,
and red potatoes, made by Dr. Neubert. These were made by uniting not
the tubers but the young stems, as was done by Mr. Fitzpatrick. The
result was remarkable, inasmuch as all the tubers thus produced were
intermediate in character, though in a variable degree. Those between
the black and the white or the red were the most striking in
appearance. Some from between the white and red had one half of one
colour and the other half of the other colour.
At the next meeting of the society Herr Magnus communicated the results
of Dr. Heimann’s experiments in grafting together the tubers of red
Saxon, blue, and elongated white potatoes. The eyes were removed by a
cylindrical instrument, and inserted into corresponding holes in other
varieties. The plants thus produced yielded a great number of tubers,
which were intermediate between the two parent-forms in shape, and in
the colour both of the flesh and skin.
Herr Reuter experimented,[115] by inserting wedges of the elongated
White Mexican potato into a Black Kidney potato. Both sorts are known
to be very constant, and differ much not only in form and colour, but
in the eyes of the Black Kidney being deeply sunk, whereas those of the
White Mexican are superficial and of a different shape. The tubers
produced by these hybrids were intermediate in colour and form; and
some which resembled in form the graft, _i.e._ the Mexican, had eyes
deeply sunk and of the same shape as in the stock or Black Kidney.
Any one who will attentively consider the abstract now given, of the
experiments made by many observers in several countries, will, I think,
be convinced that by grafting two varieties of the potato together in
various ways, hybridised plants can be produced. It should be observed
that several of the experimentalists are scientific horticulturists,
and some of them potato-growers on a large scale, who, though
beforehand sceptical, have been fully convinced of the possibility,
even of the ease, of making graft-hybrids. The only way of escaping
from this conclusion is to attribute all the many recorded cases to
simple bud-variation. Undoubtedly the potato, as we have seen in this
chapter, does sometimes, though not often, vary by buds; but it should
be especially noted that it is experienced potato-growers, whose
business it is to look out for new varieties, who have expressed
unbounded astonishment at the number of new forms produced by
graft-hybridisation. It may be argued that it is merely the operation
of grafting, and not the union of two kinds, which causes so
extraordinary an amount of bud-variation; but this objection is at once
answered by the fact that potatoes are habitually propagated by the
tubers being cut into pieces, and the sole difference in the case of
graft-hybrids is that either a half or a smaller segment or a cylinder
is placed in close opposition with the tissue of another variety.
Moreover, in two cases, the young stems were grafted together, and the
plants thus united yielded the same results as when the tubers were
united. It is an argument of the greatest weight that when varieties
are produced by simple bud-variation, they frequently present quite new
characters; whereas in all the numerous cases above given, as Herr
Magnus likewise insists, the graft-hybrids are intermediate in
character between the two forms employed. That such a result should
follow if the one kind did not affect the other is incredible.
Characters of all kinds are affected by graft hybridisation, in
whatever way the grafting may have been effected. The plants thus
raised yield tubers which partake of the widely different colours,
form, state of surface, position and shape of the eye of the parents;
and according to two careful observers they are also intermediate in
certain constitutional peculiarities. But we should bear in mind that
in all the varieties of the potato, the tubers differ much more than
any other part.
The potato affords the best evidence of the possibility of the
formation of graft-hybrids, but we must not overlook the account given
of the origin of the famous _Cytisus adami_ by M. Adam, who had no
conceivable motive for deception, and the exactly parallel account of
the origin of the Bizzarria orange, namely by graft-hybridisation. Nor
must the cases be undervalued in which different varieties or species
of vines, hyacinths and roses, have been grafted together, and have
yielded intermediate forms. It is evident that graft-hybrids can be
made much more easily with some plants, as the potato, than with
others, for instance our common fruit trees; for these latter have been
grafted by the million during many centuries, and though the graft is
often slightly affected, it is very doubtful whether this may not be
accounted for, merely by a more or less free supply of nutriment.
Nevertheless, the cases above given seem to me to prove that under
certain unknown conditions graft-hybridisation can be effected.
Herr Magnus asserts with much truth that graft-hybrids resemble in all
respects seminal hybrids, including their great diversity of character.
There is, however, a partial exception, inasmuch as the characters of
the two parent forms are not often homogeneously blended together in
graft-hybrids. They much more commonly appear in a segregated
condition,—that is, in segments either at first, or subsequently
through reversion. It would seem that the reproductive elements are not
so completely blended by grafting as by sexual generation. But
segregation of this kind occurs by no means rarely, as will be
immediately shown, in seminal hybrids. Finally it must, I think, be
admitted that we learn from the foregoing cases a highly important
physiological fact, namely, that the elements that go to the production
of a new being, are not necessarily formed by the male and female
organs. They are present in the cellular tissue in such a state that
they can unite without the aid of the sexual organs, and thus give rise
to a new bud partaking of the characters of the two parent-forms.
_On the segregation of the parental characters in seminal hybrids by
bud-variation._—I will now give a sufficient number of cases to show
that segregation of this kind, namely, by buds, may occur in ordinary
hybrids raised from seed.
Hybrids were raised by Gärtner between _Tropæolum minus_ and
_majus_[116] which at first produced flowers intermediate in size,
colour, and structure between their two parents; but later in the
season some of these plants produced flowers in all respects like those
of the mother-form, mingled with flowers still retaining the usual
intermediate condition. A hybrid Cereus between _C. speciosissimus_ and
_phyllanthus,_[117] plants which are widely different in appearance,
produced for the first three years angular, five-sided stems, and then
some flat stems like those of _C. phyllanthus._ Kölreuter also gives
cases of hybrid Lobelias and Verbascums, which at first produced
flowers of one colour, and later in the season, flowers of a different
colour.[118] Naudin[119] raised forty hybrids from _Datura lævis_
fertilised by _D. stramonium_; and three of these hybrids produced many
capsules, of which a half, or quarter, or lesser segment was smooth and
of small size, like the capsule of the pure _D. lævis,_ the remaining
part being spinose and of larger size, like the capsule of the pure _D.
stramonium_: from one of these composite capsules, plants perfectly
resembling both parent-forms were raised.