CULTIVATED PLANTS: CEREAL AND CULINARY PLANTS.
PRELIMINARY REMARKS ON THE NUMBER AND PARENTAGE OF CULTIVATED
PLANTS--FIRST STEPS IN CULTIVATION--GEOGRAPHICAL DISTRIBUTION OF
CULTIVATED PLANTS.
CEREALIA.--DOUBTS ON THE NUMBER OF SPECIES.--WHEAT: VARIETIES
OF--INDIVIDUAL VARIABILITY--CHANGED HABITS--SELECTION--ANCIENT HISTORY
OF THE VARIETIES.--MAIZE: GREAT VARIATION OF--DIRECT ACTION OF CLIMATE
ON.
CULINARY PLANTS.--CABBAGES: VARIETIES OF, IN FOLIAGE AND STEMS, BUT NOT
IN OTHER PARTS--PARENTAGE OF--OTHER SPECIES OF BRASSICA.--PEAS: AMOUNT
OF DIFFERENCE IN THE SEVERAL KINDS, CHIEFLY IN THE PODS AND SEED--SOME
VARIETIES CONSTANT, SOME HIGHLY VARIABLE--DO NOT
INTERCROSS.--BEANS.--POTATOES: NUMEROUS VARIETIES OF--DIFFERING LITTLE,
EXCEPT IN THE TUBERS--CHARACTERS INHERITED.
I shall not enter into so much detail on the variability of cultivated
plants, as in the case of domesticated animals. The subject is involved in
much difficulty. Botanists have generally neglected cultivated varieties,
as beneath their notice. In several cases the wild prototype is unknown or
doubtfully known; and in other cases it is hardly possible to distinguish
between escaped seedlings and truly wild plants, so that there is no safe
standard of comparison by which to judge of any supposed amount of change.
Not a few botanists believe that several of our anciently cultivated plants
have become so profoundly modified that it is not possible now to recognise
their aboriginal parent-forms. Equally perplexing are the doubts whether
some of them are descended from one species, or from several inextricably
commingled by crossing and variation. Variations often pass into, and
cannot be distinguished from, monstrosities; and monstrosities are of
little significance for our purpose. Many varieties are propagated solely
by grafts, buds, layers, bulbs, &c., and frequently it is not known how far
their peculiarities can be transmitted by seminal generation. Nevertheless
some facts of value can be gleaned; and other facts will hereafter be {306}
incidentally given. One chief object in the two following chapters is to
show how generally almost every character in our cultivated plants has
become variable.
Before entering on details a few general remarks on the origin of
cultivated plants may be introduced. M. Alph. de Candolle[519] in an
admirable discussion on this subject, in which he displays a wonderful
amount of knowledge, gives a list of 157 of the most useful cultivated
plants. Of these he believes that 85 are almost certainly known in their
wild state; but on this head other competent judges[520] entertain great
doubts. Of 40 of them, the origin is admitted by M. De Candolle to be
doubtful, either from a certain amount of dissimilarity which they present
when compared with their nearest allies in a wild state, or from the
probability of the latter not being truly wild plants, but seedlings
escaped from culture. Of the entire 157, 32 alone are ranked by M. De
Candolle as quite unknown in their aboriginal condition. But it should be
observed that he does not include in his list several plants which present
ill-defined characters, namely, the various forms of pumpkins, millet,
sorghum, kidney-bean, dolichos, capsicum, and indigo. Nor does he include
flowers; and several of the more anciently cultivated flowers, such as
certain roses, the common Imperial lily, the tuberose, and even the lilac,
are said[521] not to be known in the wild state.
From the relative numbers above given, and from other arguments of much
weight, M. De Candolle concludes that plants have rarely been so much
modified by culture that they cannot be identified with their wild
prototypes. But on this view, considering that savages probably would not
have chosen rare plants for cultivation, that useful plants are generally
conspicuous, and that they could not have been the inhabitants of deserts
or of remote and recently discovered islands, it appears strange to me that
so many of our cultivated plants should be still unknown or only doubtfully
known in the wild state. If, on the other hand, many of these plants have
been profoundly modified by culture, the difficulty disappears. Their {307}
extermination during the progress of civilisation would likewise remove the
difficulty; but M. De Candolle has shown that this probably has seldom
occurred. As soon as a plant became cultivated in any country, the
half-civilised inhabitants would no longer have need to search the whole
surface of the land for it, and thus lead to its extirpation; and even if
this did occur during a famine, dormant seeds would be left in the ground.
In tropical countries the wild luxuriance of nature, as was long ago
remarked by Humboldt, overpowers the feeble efforts of man. In anciently
civilised temperate countries, where the whole face of the land has been
greatly changed, it can hardly be doubted that some plants have been
exterminated; nevertheless De Candolle has shown that all the plants
historically known to have been first cultivated in Europe still exist here
in the wild state.
MM. Loiseleur-Deslongchamps [522] and De Candolle have remarked that our
cultivated plants, more especially the cereals, must originally have
existed in nearly their present state; for otherwise they would not have
been noticed and valued as objects of food. But these authors apparently
have not considered the many accounts given by travellers of the wretched
food collected by savages. I have read an account of the savages of
Australia cooking, during a dearth, many vegetables in various ways, in the
hopes of rendering them innocuous and more nutritious. Dr. Hooker found the
half-starved inhabitants of a village in Sikhim suffering greatly from
having eaten arum-roots,[523] which they had pounded and left for several
days to ferment, so as partially to destroy their poisonous nature; and he
adds that they cooked and ate many other deleterious plants. Sir Andrew
Smith informs me that in South Africa a large number of fruits and
succulent leaves, and especially roots, are used in times of scarcity. The
natives, indeed, know the properties of a long catalogue of plants, some
having {308} been found during famines to be eatable, others injurious to
health, or even destructive to life. He met a party of Baquanas who, having
been expelled by the conquering Zulus, had lived for years on any roots or
leaves which afforded some little nutriment, and distended their stomachs,
so as to relieve the pangs of hunger. They looked like walking skeletons,
and suffered fearfully from constipation. Sir Andrew Smith also informs me
that on such occasions the natives observe as a guide for themselves, what
the wild animals, especially baboons and monkeys, eat.
From innumerable experiments made through dire necessity by the savages of
every land, with the results handed down by tradition, the nutritious,
stimulating, and medicinal properties of the most unpromising plants were
probably first discovered. It appears, for instance, at first an
inexplicable fact that untutored man, in three distant quarters of the
world, should have discovered amongst a host of native plants that the
leaves of the tea-plant and mattee, and the berries of the coffee, all
included a stimulating and nutritious essence, now known to be chemically
the same. We can also see that savages suffering from severe constipation
would naturally observe whether any of the roots which they devoured acted
as aperients. We probably owe our knowledge of the uses of almost all
plants to man having originally existed in a barbarous state, and having
been often compelled by severe want to try as food almost everything which
he could chew and swallow.
From what we know of the habits of savages in many quarters of the world,
there is no reason to suppose that our cereal plants originally existed in
their present state so valuable to man. Let us look to one continent alone,
namely, Africa: Barth[524] states that the slaves over a large part of the
central region regularly collect the seeds of a wild grass, the _Pennisetum
distichum_; in another district he saw women collecting the seeds of a Poa
by swinging a sort of basket through the rich meadow-land. Near Tete
Livingstone observed the natives collecting the seeds {309} of a wild
grass; and farther south, as Andersson informs me, the natives largely use
the seeds of a grass of about the size of canary-seed, which they boil in
water. They eat also the roots of certain reeds, and every one has read of
the Bushmen prowling about and digging up with a fire-hardened stake
various roots. Similar facts with respect to the collection of seeds of
wild grasses in other parts of the world could be given.[525]
Accustomed as we are to our excellent vegetables and luscious fruits, we
can hardly persuade ourselves that the stringy roots of the wild carrot and
parsnip, or the little shoots of the wild asparagus, or crabs, sloes, &c.,
should ever have been valued; yet, from what we know of the habits of
Australian and South African savages, we need feel no doubt on this head.
The inhabitants of Switzerland during the Stone-period largely collected
wild crabs, sloes, bullaces, hips of roses, elderberries, beech-mast, and
other wild berries and fruit.[526] Jemmy Button, a Fuegian on board the
_Beagle_, remarked to me that the poor and acid black-currants of Tierra
del Fuego were too sweet for his taste.
The savage inhabitants of each land, having found out by many and hard
trials what plants were useful, or could be rendered useful by various
cooking processes, would after a time take the first step in cultivation by
planting them near their usual abodes. Livingstone[527] states that the
savage Batokas sometimes left wild fruit-trees standing in their gardens,
and occasionally even planted them, "a practice seen nowhere else amongst
the natives." But Du Chaillu saw a palm and some other wild fruit-trees
which had been planted; and these trees were considered private property.
The next step in cultivation, and this would require but little
forethought, would be to sow {310} the seeds of useful plants; and as the
soil near the hovels of the natives[528] would often be in some degree
manured, improved varieties would sooner or later arise. Or a wild and
unusually good variety of a native plant might attract the attention of
some wise old savage; and he would transplant it, or sow its seed. That
superior varieties of wild fruit-trees occasionally are found is certain,
as in the case of the American species of hawthorns, plums, cherries,
grapes, and hickories, specified by Professor Asa Gray.[529] Downing also
refers to certain wild varieties of the hickory, as being "of much larger
size and finer flavour than the common species." I have referred to
American fruit-trees, because we are not in this case troubled with doubts
whether or not the varieties are seedlings which have escaped from
cultivation. Transplanting any superior variety, or sowing its seeds,
hardly implies more forethought than might be expected at an early and rude
period of civilisation. Even the Australian barbarians "have a law that no
plant bearing seeds is to be dug up after it has flowered;" and Sir G.
Grey[530] never saw this law, evidently framed for the preservation of the
plant, violated. We see the same spirit in the superstitious belief of the
Fuegians, that killing water-fowl whilst very young will be followed by
"much rain, snow, blow much."[531] I may add, as showing forethought in the
lowest barbarians, that the Fuegians when they find a stranded whale bury
large portions in the sand, and during the often-recurrent famines travel
from great distances for the remnants of the half-putrid mass.
It has often been remarked[532] that we do not owe a single useful plant to
Australia or the Cape of Good Hope,--countries abounding to an unparalleled
degree with endemic species,--or to New Zealand, or to America south of the
Plata; and, according to some authors, not to America northward of Mexico.
I do not believe that any edible or valuable plant, except the {311}
canary-grass, has been derived from an oceanic or uninhabited island. If
nearly all our useful plants, natives of Europe, Asia, and South America,
had originally existed in their present condition, the complete absence of
similarly useful plants in the great countries just named would indeed be a
surprising fact. But if these plants have been so greatly modified and
improved by culture as no longer closely to resemble any natural species,
we can understand why the above-named countries have given us no useful
plants, for they were either inhabited by men who did not cultivate the
ground at all, as in Australia and the Cape of Good Hope, or who cultivated
it very imperfectly, as in some parts of America. These countries do yield
plants which are useful to savage man; and Dr. Hooker[533] enumerates no
less than 107 such species in Australia alone; but these plants have not
been improved, and consequently cannot compete with those which have been
cultivated and improved during thousands of years in the civilised world.
The case of New Zealand, to which fine island we as yet owe no widely
cultivated plant, may seem opposed to this view; for, when first
discovered, the natives cultivated several plants; but all inquirers
believe, in accordance with the traditions of the natives, that the early
Polynesian colonists brought with them seeds and roots, as well as the dog,
which had all been wisely preserved during their long voyage. The
Polynesians are so frequently lost on the ocean, that this degree of
prudence would occur to any wandering party: hence the early colonists of
New Zealand, like the later European colonists, would not have had any
strong inducement to cultivate the aboriginal plants. According to De
Candolle we owe thirty-three useful plants to Mexico, Peru, and Chile; nor
is this surprising when we remember the civilized state of the inhabitants,
as shown by the fact of their having practised artificial irrigation and
made tunnels through hard rocks without the use of iron or gunpowder, and
who, as we shall see in a future chapter, fully recognised, as far as
animals were concerned, and therefore probably in the case of plants, the
important principle of selection. We owe some plants to Brazil; and the
early voyagers, namely Vespucius and Cabral, describe the country as
thickly peopled {312} and cultivated. In North America[534] the natives
cultivated maize, pumpkins, gourds, beans, and peas, "all different from
ours," and tobacco; and we are hardly justified in assuming that none of
our present plants are descended from these North American forms. Had North
America been civilized for as long a period, and as thickly peopled, as
Asia or Europe, it is probable that the native vines, walnuts, mulberries,
crabs, and plums, would have given rise, after a long course of
cultivation, to a multitude of varieties, some extremely different from
their parent-stocks; and escaped seedlings would have caused in the New, as
in the Old World, much perplexity with respect to their specific
distinctness and parentage.[535]
_Cerealia._--I will now enter on details. The cereals cultivated in
Europe consist of four genera--wheat, rye, barley, and oats. Of wheat
the best modern authorities[536] make four or five, or even seven
distinct species; of rye, one; of barley, three; and of oats, two,
three, or four species. So that altogether our cereals are ranked by
different authors under from ten to fifteen distinct species. These
have given rise to a multitude of varieties. It is a remarkable fact
that botanists are not universally agreed on the aboriginal parent-form
of any one cereal plant. For instance, a high authority writes in
1855,[537] "We ourselves have no hesitation in stating our conviction,
as the result of all the most reliable evidence, that none of these
Cerealia exist, or have existed, truly wild in their present state, but
that all are cultivated varieties of species now growing in great
abundance in S. Europe or W. Asia." On the other hand, Alph. De
Candolle[538] has adduced abundant evidence that common wheat
(_Triticum vulgare_) has been found wild in various parts of Asia,
where it is not likely to have escaped from cultivation; and there is
{313} force in M. Godron's remark, that, supposing these plants to be
escaped seedlings,[539] if they have propagated themselves in a wild
state for several generations, their continued resemblance to
cultivated wheat renders it probable that the latter has retained its
aboriginal character. M. De Candolle insists strongly on the frequent
occurrence in the Austrian dominions of rye and of one kind of oats in
an apparently wild condition. With the exception of these two cases,
which however are rather doubtful, and with the exception of two forms
of wheat and one of barley, which he believes to have been found truly
wild, M. De Candolle does not seem fully satisfied with the other
reported discoveries of the parent-forms of our other cereals. With
respect to oats, according to Mr. Buckman,[540] the wild English _Avena
fatua_ can be converted by a few years of careful cultivation and
selection into forms almost identical with two very distinct cultivated
races. The whole subject of the origin and specific distinctness of the
various cereal plants is a most difficult one; but we shall perhaps be
able to judge a little better after considering the amount of variation
which wheat has undergone.
Metzger describes seven species of wheat, Godron refers to five, and De
Candolle to only four. It is not improbable that, besides the kinds
known in Europe, other strongly characterised forms exist in the more
distant parts of the world; for Loiseleur-Deslongchamps[541] speaks of
three new species or varieties, sent to Europe in 1822 from Chinese
Mongolia, which he considers as being there indigenous. Moorcroft[542]
also speaks of Hasora wheat in Ladakh as very peculiar. If those
botanists are right who believe that at least seven species of wheat
originally existed, then the amount of variation in any important
character which wheat has undergone under cultivation has been slight;
but if only four or a lesser number of species originally existed, then
it is evident that varieties so strongly marked have arisen, that they
have been considered by capable judges as specifically distinct. But
the impossibility of deciding which forms ought to be ranked as species
and which as varieties, makes it useless to specify in detail the
differences between the various kinds of wheat. Speaking generally, the
organs of vegetation differ little;[543] but some kinds grow close and
upright, whilst others spread and trail along the ground. The straw
differs in being more or less hollow, and in quality. The ears[544]
{314} differ in colour and in shape, being quadrangular, compressed, or
nearly cylindrical; and the florets differ in their approximation to
each other, in their pubescence, and in being more or less elongated.
The presence or absence of barbs is a conspicuous difference, and in
certain Gramineae serves even as a generic character;[545] although, as
remarked by Godron,[546] the presence of barbs is variable in certain
wild grasses, and especially in those, such as _Bromus secalinus_ and
_Lolium temulentum_, which habitually grow mingled with our cereal
crops, and which have thus unintentionally been exposed to culture. The
grains differ in size, weight, and colour; in being more or less downy
at one end, in being smooth or wrinkled, in being either nearly
globular, oval, or elongated; and finally in internal texture, being
tender or hard, or even almost horny, and in the proportion of gluten
which they contain.
Nearly all the races or species of wheat vary, as Godron[547] has
remarked, in an exactly parallel manner,--in the seed being downy or
glabrous, and in colour,--and in the florets being barbed or not
barbed, &c. Those who believe that all the kinds are descended from a
single wild species may account for this parallel variation by the
inheritance of a similar constitution, and a consequent tendency to
vary in the same manner; and those who believe in the general theory of
descent with modification may extend this view to the several species
of wheat, if such ever existed in a state of nature.
Although few of the varieties of wheat present any conspicuous
difference, their number is great. Dalbret cultivated during thirty
years from 150 to 160 kinds, and excepting in the quality of the grain
they all kept true: Colonel Le Couteur possessed upwards of 150, and
Philippar 322 varieties.[548] As wheat is an annual, we thus see how
strictly many trifling differences in character are inherited through
many generations. Colonel Le Couteur insists strongly on this same
fact: in his persevering and successful attempts to raise new varieties
by selection, he began by choosing the best ears, but soon found that
the grains in the same ear differed so that he was compelled to select
them separately; and each grain generally transmitted its own
character. The great amount of variability in the plants of the same
variety is another interesting point, which would never have been
detected except by an eye long practised to the work; thus Colonel Le
Couteur relates[549] that in a field of his own wheat, which he
considered at least as pure as that of any of his neighbours, Professor
La Gasca found twenty-three sorts; and Professor Henslow has observed
similar facts. Besides such individual variations, forms sufficiently
well marked to be valued and to become widely cultivated {315}
sometimes suddenly appear: thus Mr. Sheriff has had the good fortune to
raise in his lifetime seven new varieties, which are now extensively
grown in many parts of Britain.[550]
As in the case of many other plants, some varieties, both old and new,
are far more constant in character than others. Colonel Le Couteur was
forced to reject some of his new sub-varieties, which he suspected had
been produced from a cross, as incorrigibly sportive. With respect to
the tendency to vary, Metzger[551] gives from his own experience some
interesting facts: he describes three Spanish sub-varieties, more
especially one known to be constant in Spain, which in Germany assumed
their proper character only during hot summers; another variety kept
true only in good land, but after having been cultivated for
twenty-five years became more constant. He mentions two other
sub-varieties which were at first inconstant, but subsequently became,
apparently without any selection, accustomed to their new homes, and
retained their proper character. These facts show what small changes in
the conditions of life cause variability, and they further show that a
variety may become habituated to new conditions. One is at first
inclined to conclude with Loiseleur-Deslongchamps, that wheat
cultivated in the same country is exposed to remarkably uniform
conditions; but manures differ, seed is taken from one soil to another,
and what is far more important the plants are exposed as little as
possible to struggle with other plants, and are thus enabled to exist
under diversified conditions. In a state of nature each plant is
confined to that particular station and kind of nutriment which it can
seize from the other plants by which it is surrounded.
Wheat quickly assumes new habits of life. The summer and winter kinds
were classed by Linnaeus as distinct species; but M. Monnier[552] has
proved that the difference between them is only temporary. He sowed
winter-wheat in spring, and out of one hundred plants four alone
produced ripe seeds; these were sown and resown, and in three years
plants were reared which ripened all their seed. Conversely, nearly all
the plants raised from summer-wheat, which was sown in autumn, perished
from frost; but a few were saved and produced seed, and in three years
this summer-variety was converted into a winter-variety. Hence it is
not surprising that wheat soon becomes to a certain extent
acclimatised, and that seed brought from distant countries and sown in
Europe vegetates at first, or even for a considerable period,[553]
differently from our European varieties. In Canada the first settlers,
according to Kalm,[554] found their winters too severe for winter-wheat
brought from France, and their summers often too short for
summer-wheat; and until they procured summer-wheat from the northern
parts of Europe, which succeeded well, they thought that their {316}
country was useless for corn crops. It is notorious that the proportion
of gluten differs much under different climates. The weight of the
grain is also quickly affected by climate: Loiseleur-Deslongchamps[555]
sowed near Paris 54 varieties, obtained from the South of France and
from the Black Sea, and 52 of these yielded seed from 10 to 40 per
cent. heavier than the parent-seed. He then sent these heavier grains
back to the South of France, but there they immediately yielded lighter
seed.
All those who have closely attended to the subject insist on the close
adaptation of numerous varieties of wheat to various soils and climates
even within the same country; thus Colonel Le Couteur[556] says, "It is
the suitableness of each sort to each soil that will enable the farmer
to pay his rent by sowing one variety, where he would be unable to do
so by attempting to grow another of a seemingly better sort." This may
be in part due to each kind becoming habituated to its conditions of
life, as Metzger has shown certainly occurs, but it is probably in main
part due to innate differences between the several varieties.
Much has been written on the deterioration of wheat; that the quality
of the flour, size of grain, time of flowering, and hardiness may be
modified by climate and soil, seems nearly certain; but that the whole
body of any one sub-variety ever becomes changed into another and
distinct sub-variety, there is no reason to believe. What apparently
does take place, according to Le Couteur,[557] is, that some one
sub-variety out of the many which may always be detected in the same
field is more prolific than the others, and gradually supplants the
variety which was first sown.
With respect to the natural crossing of distinct varieties the evidence
is conflicting, but preponderates against its frequent occurrence. Many
authors maintain that impregnation takes place in the closed flower,
but I am sure from my own observations that this is not the case, at
least with those varieties to which I have attended. But as I shall
have to discuss this subject in another work, it may be here passed
over.
In conclusion, all authors admit that numerous varieties of wheat have
arisen; but their differences are unimportant, unless, indeed, some of the
so-called species are ranked as varieties. Those who believe that from four
to seven wild species of Triticum originally existed in nearly the same
condition as at present, rest their belief chiefly on the great antiquity
of the several forms.[558] It is an important fact, which we have recently
learnt from the admirable researches {317} of Heer,[559] that the
inhabitants of Switzerland, even so early as the Neolithic period,
cultivated no less than ten cereal plants, namely, five kinds of wheat, of
which at least four are commonly looked at as distinct species, three kinds
of barley, a panicum, and a setaria. If it could be shown that at the
earliest dawn of agriculture five kinds of wheat and three of barley had
been cultivated, we should of course be compelled to look at these forms as
distinct species. But, as Heer has remarked, agriculture even at the period
of the lake-habitations had already made considerable progress; for,
besides the ten cereals, peas, poppies, flax, and apparently apples, were
cultivated. It may also be inferred, from one variety of wheat being the
so-called Egyptian, and from what is known of the native country of the
panicum and setaria, as well as from the nature of the weeds which then
grew mingled with the crops, that the lake-inhabitants either still kept up
commercial intercourse with some southern people or had originally
proceeded as colonists from the South.
Loiseleur-Deslongchamps[560] has argued that, if our cereal plants had been
greatly modified by cultivation, the weeds which habitually grow mingled
with them would have been equally modified. But this argument shows how
completely the principle of selection has been overlooked. That such weeds
have not varied, or at least do not vary now in any extreme degree, is the
opinion of Mr. H. C. Watson and Professor Asa Gray, as they inform me; but
who will pretend to say that they do not vary as much as the individual
plants of the same sub-variety of wheat? We have already seen that pure
varieties of wheat, cultivated in the same field, offer many slight
variations, which can be selected and separately propagated; and that
occasionally more strongly pronounced variations appear, which, as Mr.
Sheriff has proved, are well worthy of extensive cultivation. Not until
equal attention be paid to the variability and selection of weeds, can the
argument from their constancy under unintentional culture be of any value.
In accordance with the principles of selection we can understand how it is
that in the several cultivated varieties of wheat the organs of vegetation
differ so little; for if a plant {318} with peculiar leaves appeared, it
would be neglected unless the grains of corn were at the same time superior
in quality or size. The selection of seed-corn was strongly
recommended[561] in ancient times by Columella and Celsus; and as Virgil
says,--
"I've seen the largest seeds, tho' view'd with care,
Degenerate, unless th' industrious hand
Did yearly cull the largest."
But whether in ancient times selection was methodically pursued we may well
doubt, when we hear how laborious the work was found by Le Couteur.
Although the principle of selection is so important, yet the little which
man has effected, by incessant efforts[562] during thousands of years, in
rendering the plants more productive or the grains more nutritious than
they were in the time of the old Egyptians, would seem to speak strongly
against its efficacy. But we must not forget that at each successive period
the state of agriculture and the quantity of manure supplied to the land
will have determined the maximum degree of productiveness; for it would be
impossible to cultivate a highly productive variety, unless the land
contained a sufficient supply of the necessary chemical elements.
We now know that man was sufficiently civilized to cultivate the ground at
an immensely remote period; so that wheat might have been improved long ago
up to that standard of excellence which was possible under the then
existing state of agriculture. One small class of facts supports this view
of the slow and gradual improvement of our cereals. In the most ancient
lake-habitations of Switzerland, when men employed only flint-tools, the
most extensively cultivated wheat was a peculiar kind, with remarkably
small ears and grains.[563] "Whilst the grains of the modern forms are in
section from seven to eight millimetres in length, the larger grains from
the lake-habitations are six, seldom seven, and the smaller ones only four.
The ear is thus much narrower, and the spikelets stand out more
horizontally, than in our present forms." So again with barley, the most
ancient and most extensively cultivated kind had small ears, and the grains
{319} were "smaller, shorter, and nearer to each other, than in that now
grown; without the husk they were 21/2 lines long, and scarcely 11/2 broad,
whilst those now grown have a length of three lines, and almost the same in
breadth."[564] These small-grained varieties of wheat and barley are
believed by Heer to be the parent-forms of certain existing allied
varieties, which have supplanted their early progenitors.
Heer gives an interesting account of the first appearance and final
disappearance of the several plants which were cultivated in greater or
less abundance in Switzerland during former successive periods, and which
generally differed more or less from our existing varieties. The peculiar
small-eared and small-grained wheat, already alluded to, was the commonest
kind during the Stone period; it lasted down to the Helvetico-Roman age,
and then became extinct. A second kind was rare at first, but afterwards
became more frequent. A third, the Egyptian wheat (_T. turgidum_), does not
agree exactly with any existing variety, and was rare during the Stone
period. A fourth kind (_T. dicoccum_) differs from all known varieties of
this form. A fifth kind (_T. monococcum_) is known to have existed during
the Stone period only by the presence of a single ear. A sixth kind, the
common _T. spelta_, was not introduced into Switzerland until the Bronze
age. Of barley, besides the short-eared and small-grained kind, two others
were cultivated, one of which was very scarce, and resembled our present
common _H. distichum_. During the Bronze age rye and oats were introduced;
the oat-grains being somewhat smaller than those produced by our existing
varieties. The poppy was largely cultivated during the Stone period,
probably for its oil; but the variety which then existed is not now known.
A peculiar pea with small seeds lasted from the Stone to the Bronze age,
and then became extinct; whilst a peculiar bean, likewise having small
seeds, came in at the Bronze period and lasted to the time of the Romans.
These details sound like the description given by a palaeontologist of the
mutations in form, of the first appearance, the increasing rarity, and
final extinction of fossil species, embedded in the successive stages of a
geological formation.
{320}
Finally, every one must judge for himself whether it is more probable that
the several forms of wheat, barley, rye, and oats are descended from
between ten and fifteen species, most of which are now either unknown or
extinct, or whether they are descended from between four and eight species,
which may have either closely resembled our present cultivated forms, or
have been so widely different as to escape identification. In this latter
case, we must conclude that man cultivated the cereals at an enormously
remote period, and that he formerly practised some degree of selection,
which in itself is not improbable. We may, perhaps, further believe that,
when wheat was first cultivated, the ears and grains increased quickly in
size, in the same manner as the roots of the wild carrot and parsnip are
known to increase quickly in bulk under cultivation.
_Maize: Zea Mays._--Botanists are nearly unanimous that all the
cultivated kinds belong to the same species. It is undoubtedly[565] of
American origin, and was grown by the aborigines throughout the
continent from New England to Chili. Its cultivation must have been
extremely ancient, for Tschudi[566] describes two kinds, now extinct or
not known in Peru, which were taken from tombs apparently prior to the
dynasty of the Incas. But there is even stronger evidence of antiquity,
for I found on the coast of Peru[567] heads of maize, together with
eighteen species of recent sea-shell, embedded in a beach which had
been upraised at least 85 feet above the level of the sea. In
accordance with this ancient cultivation, numerous American varieties
have arisen. The aboriginal form has not as yet been discovered in the
wild state. A peculiar kind,[568] in which the grains, instead of being
naked, are concealed by husks as much as eleven lines in length, has
been stated on insufficient evidence to grow wild in Brazil. It is
almost certain that the aboriginal form would have had its grains thus
protected;[569] but the seeds of the Brazilian variety produce, as I
hear from Professor Asa Gray, and as is stated in two published
accounts, either common or husked maize; and it is not {321} credible
that a wild species, when first cultivated, should vary so quickly and
in so great a degree.
Maize has varied in an extraordinary and conspicuous manner.
Metzger,[570] who paid particular attention to the cultivation of this
plant, makes twelve races (unter-art) with numerous sub-varieties; of
the latter some are tolerably constant, others quite inconstant. The
different races vary in height from 15-18 feet to only 16-18 inches, as
in a dwarf variety described by Bonafous. The whole ear is variable in
shape, being long and narrow, or short and thick, or branched. The ear
in one variety is more than four times as long as in a dwarf kind. The
seeds are arranged in the ear in from six to even twenty rows, or are
placed irregularly. The seeds are coloured--white, pale-yellow, orange,
red, violet, or elegantly streaked with black;[571] and in the same ear
there are sometimes seeds of two colours. In a small collection I found
that a single grain of one variety nearly equalled in weight seven
grains of another variety. The shape of the seed varies greatly, being
very flat, or nearly globular, or oval; broader than long, or longer
than broad; without any point, or produced into a sharp tooth, and this
tooth is sometimes recurved. One variety (the rugosa of Bonafous) has
its seeds curiously wrinkled, giving to the whole ear a singular
appearance. Another variety (the cymosa of Bon.) carries its ears so
crowded together that it is called _mais a bouquet_. The seeds of some
varieties contain much glucose instead of starch. Male flowers
sometimes appear amongst the female flowers, and Mr. J. Scott has
lately observed the rarer case of female flowers on a true male
panicle, and likewise hermaphrodite flowers.[572] Azara describes[573]
a variety in Paraguay the grains of which are very tender, and he
states that several varieties are fitted for being cooked in various
ways. The varieties also differ greatly in precocity, and have
different powers of resisting dryness and the action of violent
wind.[574] Some of the foregoing differences would certainly be
considered of specific value with plants in a state of nature.
Le Comte Re states that the grains of all the varieties which he
cultivated ultimately assumed a yellow colour. But Bonafous[575] found
that most of those which he sowed for ten consecutive years kept true
to their proper tints; and he adds that in the valleys of the Pyrenees
and on the plains of Piedmont a white maize has been cultivated for
more than a century, and has undergone no change.
The tall kinds grown in southern latitudes, and therefore exposed to
great heat, require from six to seven months to ripen their seed;
whereas the dwarf kinds, grown in northern and colder climates, require
only from {322} three to four months.[576] Peter Kalm,[577] who
particularly attended to this plant, says, that in the United States,
in proceeding from south to north, the plants steadily diminish in
bulk. Seeds brought from lat. 37 deg. in Virginia, and sown in lat. 43 deg.-44 deg.
in New England, produce plants which will not ripen their seed, or
ripen them with the utmost difficulty. So it is with seed carried from
New England to lat. 45 deg.-47 deg. in Canada. By taking great care at first,
the southern kinds after some years' culture ripen their seed perfectly
in their northern homes, so that this is an analogous case with that of
the conversion of summer into winter wheat, and conversely. When tall
and dwarf maize are planted together, the dwarf kinds are in full
flower before the others have produced a single flower; and in
Pennsylvania they ripen their seed six weeks earlier than the tall
maize. Metzger also mentions a European maize which ripens its seed
four weeks earlier than another European kind. With these facts, so
plainly showing inherited acclimatisation, we may readily believe Kalm,
who states that in North America maize and some other plants have
gradually been cultivated further and further northward. All writers
agree that to keep the varieties of maize pure they must be planted
separately so that they shall not cross.
The effects of the climate of Europe on the American varieties is
highly remarkable. Metzger obtained seed from various parts of America,
and cultivated several kinds in Germany. I will give an abstract of the
changes observed[578] in one case, namely, with a tall kind
(Breit-korniger mays, Zea altissima) brought from the warmer parts of
America. During the first year the plants were twelve feet high, and
few seeds were perfected; the lower seeds in the ear kept true to their
proper form, but the upper seeds became slightly changed. In the second
generation the plants were from nine to ten feet in height, and ripened
their seed better; the depression on the outer side of the seed had
almost disappeared, and the original beautiful white colour had become
duskier. Some of the seeds had even become yellow, and in their now
rounded form they approached common European maize. In the third
generation nearly all resemblance to the original and very distinct
American parent-form was lost. In the sixth generation this maize
perfectly resembled a European variety, described as the second
sub-variety of the fifth race. When Metzger published his book, this
variety was still cultivated near Heidelberg, and could be
distinguished from the common kind only by a somewhat more vigorous
growth. Analogous results were obtained by the cultivation of another
American race, the "white-tooth corn," in which the tooth nearly
disappeared even in the second generation. A third race, the
"chicken-corn," did not undergo so great a change, but the seeds became
less polished and pellucid.
These facts afford the most remarkable instance known to me of the direct
and prompt action of climate on a plant. It might {323} have been expected
that the tallness of the stem, the period of vegetation, and the ripening
of the seed, would have been thus affected; but it is a much more
surprising fact that the seeds should have undergone so rapid and great a
change. As, however, flowers, with their product the seed, are formed by
the metamorphosis of the stem and leaves, any modification in these latter
organs would be apt to extend, through correlation, to the organs of
fructification.
_Cabbage_ (_Brassica oleracea_).--Every one knows how greatly the
various kinds of cabbage differ in appearance. In the island of Jersey,
from the effects of particular culture and of climate, a stalk has
grown to the height of sixteen feet, and "had its spring shoots at the
top occupied by a magpie's nest:" the woody stems are not unfrequently
from ten to twelve feet in height, and are there used as rafters[579]
and as walking-sticks. We are thus reminded that in certain countries
plants belonging to the generally herbaceous order of the Cruciferae are
developed into trees. Every one can appreciate the difference between
green or red cabbages with great single heads; Brussel-sprouts with
numerous little heads; broccolis and cauliflowers with the greater
number of their flowers in an aborted condition, incapable of producing
seed, and borne in a dense corymb instead of an open panicle; savoys
with their blistered and wrinkled leaves; and borecoles and kales,
which come nearest to the wild parent-form. There are also various
frizzled and laciniated kinds, some of such beautiful colours that
Vilmorin in his Catalogue of 1851 enumerates ten varieties, valued
solely for ornament, which are propagated by seed. Some kinds are less
commonly known, such as the Portuguese Couve Tronchuda, with the ribs
of its leaves greatly thickened; and the Kohlrabi or choux-raves, with
their stems enlarged into great turnip-like masses above the ground;
and the recently formed new race[580] of choux-raves, already including
nine sub-varieties, in which the enlarged part lies beneath the ground
like a turnip.
Although we see such great differences in the shape, size, colour,
arrangement, and manner of growth of the leaves and stem, and of the
flower-stems in the broccoli and cauliflower, it is remarkable that the
flowers themselves, the seed-pods, and seeds, present extremely slight
differences or none at all.[581] I compared the flowers of all the
principal kinds; those of the Couve Tronchuda are white and rather
smaller than in common cabbages; those of the Portsmouth broccoli have
narrower sepals, and smaller, less elongated petals; and in no other
cabbage could any difference be detected. With respect to the
seed-pods, in the purple Kohlrabi alone, {324} do they differ, being a
little longer and narrower than usual. I made a collection of the seeds
of twenty-eight different kinds, and most of them were
undistinguishable; when there was any difference it was excessively
slight; thus, the seeds of various broccolis and cauliflowers, when
seen in mass, are a little redder; those of the early green Ulm savoy
are rather smaller; and those of the Breda kail slightly larger than
usual, but not larger than the seeds of the wild cabbage from the coast
of Wales. What a contrast in the amount of difference is presented if,
on the one hand, we compare the leaves and stems of the various kinds
of cabbage with their flowers, pods, and seeds, and on the other hand
the corresponding parts in the varieties of maize and wheat! The
explanation is obvious; the seeds alone are valued in our cereals, and
their variations have been selected; whereas the seeds, seed-pods, and
flowers have been utterly neglected in the cabbage, whilst many useful
variations in their leaves and stems have been noticed and preserved
from an extremely remote period, for cabbages were cultivated by the
old Celts.[582]
It would be useless to give a classified description[583] of the
numerous races, sub-races, and varieties of the cabbage; but it may be
mentioned that Dr. Lindley has lately proposed[584] a system founded on
the state of development of the terminal and lateral leaf-buds, and of
the flower-buds. Thus, I. All the leaf-buds active and open, as in the
wild-cabbage, kail, &c. II. All the leaf-buds active, but forming
heads, as in Brussel-sprouts, &c. III. Terminal leaf-bud alone active,
forming a head as in common cabbages, savoys, &c. IV. Terminal leaf-bud
alone active and open, with most of the flowers abortive and succulent,
as in the cauliflower and broccoli. V. All the leaf-buds active and
open, with most of the flowers abortive and succulent, as in the
sprouting-broccoli. This latter variety is a new one, and bears the
same relation to common broccoli, as Brussel-sprouts do to common
cabbages; it suddenly appeared in a bed of common broccoli, and was
found faithfully to transmit its newly-acquired and remarkable
characters.
The principal kinds of cabbage existed at least as early as the
sixteenth century,[585] so that numerous modifications of structure
have been inherited for a long period. This fact is the more remarkable
as great care must be taken to prevent the crossing of the different
kinds. To give one proof of this: I raised 233 seedlings from cabbages
of different kinds, which had purposely been planted near each other,
and of the seedlings no less than 155 were plainly deteriorated and
mongrelized; nor were the remaining 78 all perfectly true. It may be
doubted whether many permanent varieties have been formed by
intentional or accidental crosses; for such crossed plants are found to
be very inconstant. One kind, however, called "Cottager's Kale," has
lately been produced by crossing common kale and Brussel-sprouts,
recrossed with purple broccoli,[586] and is said to be true, but plants
{325} raised by me were not nearly so constant in character as any
common cabbage.
Although most of the kinds keep true if carefully preserved from
crossing, yet the seed-beds must be yearly examined, and a few
seedlings are generally found false; but even in this case the force of
inheritance is shown, for, as Metzger has remarked[587] when speaking
of Brussel-sprouts, the variations generally keep to their "unter art,"
or main race. But in order that any kind may be truly propagated there
must be no great change in the conditions of life; thus cabbages will
not form heads in hot countries, and the same thing has been observed
with an English variety grown during an extremely warm and damp autumn
near Paris.[588] Extremely poor soil also affects the characters of
certain varieties.
Most authors believe that all the races are descended from the wild
cabbage found on the western shores of Europe; but Alph. De
Candolle[589] forcibly argues on historical and other grounds that it
is more probable that two or three closely allied forms, generally
ranked as distinct species, still living in the Mediterranean region,
are the parents, now all commingled together, of the various cultivated
kinds. In the same manner as we have often seen with domesticated
animals, the supposed multiple origin of the cabbage throws no light on
the characteristic differences between the cultivated forms. If our
cabbages are the descendants of three or four distinct species, every
trace of any sterility which may originally have existed between them
is now lost, for none of the varieties can be kept distinct without
scrupulous care to prevent intercrossing.
The other cultivated forms of the genus Brassica are descended,
according to the view adopted by Godron and Metzger,[590] from two
species, _B. napus_ and _rapa_; but according to other botanists from
three species; whilst others again strongly suspect that all these
forms, both wild and cultivated, ought to be ranked as a single
species. _Brassica napus_ has given rise to two large groups, namely,
Swedish turnips (by some believed to be of hybrid origin)[591] and
Colzas, the seeds of which yield oil. _Brassica rapa_ (of Koch) has
also given rise to two races, namely, common turnips and the oil-giving
rape. The evidence is unusually clear that these latter plants, though
so different in external appearance, belong to the same species; for
the turnip has been observed by Koch and Godron to lose its thick roots
in uncultivated soil, and when rape and turnips are sown together they
cross to such a degree that scarcely a single plant comes true.[592]
Metzger by culture converted the biennial or winter rape into the
annual or summer rape,--varieties which have been thought by some
authors to be specifically distinct.[593]
In the production of large, fleshy, turnip-like stems, we have a case
{326} of analogous variation in three forms which are generally
considered as distinct species. But scarcely any modification seems so
easily acquired as a succulent enlargement of the stem or root--that is
a store of nutriment laid up for the plant's own future use. We see
this in our radishes, beet, and in the less generally known
"turnip-rooted" celery, and in the finocchio or Italian variety of the
common fennel. Mr. Buckman has lately proved by his interesting
experiments how quickly the roots of the wild parsnip can be enlarged,
as Vilmorin formerly proved in the case of the carrot.[594] This latter
plant, in its cultivated state, differs in scarcely any character from
the wild English species, except in general luxuriance and in the size
and quality of its roots; but in the root ten varieties, differing in
colour, shape, and quality, are cultivated[595] in England, and come
true by seed. Hence, with the carrot, as in so many other cases, for
instance with the numerous varieties and sub-varieties of the radish,
that part of the plant which is valued by man, falsely appears alone to
have varied. The truth is that variations in this part alone have been
selected; and the seedlings inheriting a tendency to vary in the same
way, analogous modifications have been again and again selected, until
at last a great amount of change has been effected.
_Pea_ (_Pisum sativum_).--Most botanists look at the garden-pea as
specifically distinct from the field-pea (_P. arvense_). The latter
exists in a wild state in Southern Europe; but the aboriginal parent of
the garden-pea has been found by one collector alone, as he states, in
the Crimea.[596] Andrew Knight crossed, as I am informed by the Rev. A.
Fitch, the field-pea with a well-known garden variety, the Prussian
pea, and the cross seems to have been perfectly fertile. Dr. Alefeld
has recently studied[597] the genus with care, and, after having
cultivated about fifty varieties, concludes that they all certainly
belong to the same species. It is an interesting fact already alluded
to, that, according to O. Heer,[598] the peas found in the
lake-habitations of Switzerland of the Stone and Bronze ages, belong to
an extinct variety, with exceedingly small seeds, allied to _P.
arvense_, or field-pea. The varieties of the common garden-pea are
numerous, and differ considerably from each other. For comparison I
planted at the same time forty-one English and French varieties, and in
this one case I will describe minutely their differences. The varieties
{327} differ greatly in height,--namely from between 6 and 12 inches to
8 feet,[599]--in manner of growth, and in period of maturity. Some
varieties differ in general aspect even while only two or three inches
in height. The stems of the _Prussian_ pea are much branched. The tall
kinds have larger leaves than the dwarf kinds, but not in strict
proportion to their height:--_Hairs' Dwarf Monmouth_ has very large
leaves, and the _Pois nain hatif_, and the moderately tall _Blue
Prussian_, have leaves about two-thirds of the size of the tallest
kind. In the _Danecroft_ the leaflets are rather small and a little
pointed; in the _Queen of Dwarfs_ rather rounded; and in the _Queen of
England_ broad and large. In these three peas the slight differences in
the shape of the leaves are accompanied by slight differences in
colour. In the _Pois geant sans parchemin_, which bears purple flowers,
the leaflets in the young plant are edged with red; and in all the peas
with purple flowers the stipules are marked with red.
In the different varieties, one or two, or several flowers in a small
cluster, are borne on the same peduncle; and this is a difference which
with some of the Leguminosae is considered of specific value. In all the
varieties the flowers closely resemble each other except in colour and
size. They are generally white, sometimes purple, but the colour is
inconstant even in the same variety. In _Warner's Emperor_, which is a
tall kind, the flowers are nearly double the size of those of the _Pois
nain hatif_, but _Hairs' Dwarf Monmouth_, which has large leaves,
likewise has large flowers. The calyx in the _Victoria Marrow_ is
large, and in _Bishop's Long Pod_ the sepals are rather narrow. In no
other kind is there any difference in the flower.
The pods and seeds, which with natural species afford such constant
characters, differ greatly in the cultivated varieties of the pea; and
these are the valuable, and consequently the selected parts. _Sugar
peas_, or _Pois sans parchemin_, are remarkable from their thin pods,
which, whilst young, are cooked and eaten whole; and in this group,
which, according to Mr. Gordon includes eleven sub-varieties, it is the
pod which differs most: thus _Lewis's Negro-podded pea_ has a straight,
broad, smooth, and dark-purple pod, with the husk not so thin as in the
other kinds; the pod of another variety is extremely bowed; that of the
_Pois geant_ is much pointed at the extremity; and in the variety "_a
grands cosses_" the peas are seen through the husk in so conspicuous a
manner that the pod, especially when dry, can hardly at first be
recognised as that of a pea.
In the ordinary varieties the pods also differ much in size;--in
colour, that of _Woodford's Green Marrow_ being bright-green when dry,
instead of pale brown, and that of the purple-podded pea being
expressed by its name;--in smoothness, that of _Danecroft_ being
remarkably glossy, whereas that of the _Ne plus ultra_ is rugged;--in
being either nearly cylindrical, or broad and flat;--in being pointed
at the end as in _Thurston's Reliance_, or much truncated as in the
_American Dwarf_. In the _Auvergne pea_ the whole end of {328} the pod
is bowed upwards. In the _Queen of the Dwarfs_ and in _Scimitar peas_
the pod is almost elliptic in shape. I here give drawings of the four
most distinct pods produced by the plants cultivated by me.
[Illustration: Fig. 41.--Pods and Peas. I. Queen of Dwarfs. II.
American Dwarf. III. Thurston's Reliance. IV. Pois Geant sans
parchemin. _a._ Dan O'Rourke Pea. _b._ Queen of Dwarfs Pea. _c._
Knight's Tall White Marrow. d. Lewis's Negro Pea.]
In the pea itself we have every tint between almost pure white, brown,
yellow, and intense green; in the varieties of the _sugar peas_ we have
these same tints, together with red passing through fine purple into a
dark chocolate tint. These colours are either uniform or distributed in
dots, striae, or moss-like marks; they depend in some cases on the
colour of the cotyledons seen through the skin, and in other cases on
the outer coats of the pea itself. In the different varieties the pods
contain, according to Mr. Gordon, from eleven or twelve to only four or
five peas. The largest peas are nearly twice as much in diameter as the
smallest; and the latter are not always borne by the most dwarfed
kinds. Peas differ much in {329} shape, being smooth and spherical,
smooth and oblong, nearly oval in the _Queen of Dwarfs_, and nearly
cubical and crumpled in many of the larger kinds.
With respect to the value of the differences between the chief
varieties, it cannot be doubted that, if one of the tall _Sugar-peas_,
with purple flowers, thin-skinned pods of an extraordinary shape,
including large, dark-purple peas, grew wild by the side of the lowly
_Queen of the Dwarfs_, with white flowers, greyish-green, rounded
leaves, scimitar-like pods, containing oblong, smooth, pale-coloured
peas, which became mature at a different season; or by the side of one
of the gigantic sorts, like the _Champion of England_, with leaves of
great size, pointed pods, and large, green, crumpled, almost cubical
peas,--all three kinds would be ranked as indisputably distinct
species.
Andrew Knight[600] has observed that the varieties of peas keep very
true, because they are not crossed by insects. As far as the fact of
keeping true is concerned, I hear from Mr. Masters of Canterbury, well
known as the originator of several new kinds, that certain varieties
have remained constant for a considerable time,--for instance,
_Knight's Blue Dwarf_, which came out about the year 1820.[601] But the
greater number of varieties have a singularly short existence: thus
Loudon remarks[602] that "sorts which were highly approved in 1821, are
now, in 1833, nowhere to be found;" and on comparing the lists of 1833
with those of 1855, I find that nearly all the varieties have changed.
Mr. Masters informs me that the nature of the soil causes some
varieties to lose their character. As with other plants, certain
varieties can be propagated truly, whilst others show a determined
tendency to vary; thus two peas differing in shape, one round and the
other wrinkled, were found by Mr. Masters within the same pod, but the
plants raised from the wrinkled kind always evinced a strong tendency
to produce round peas. Mr. Masters also raised from a plant of another
variety four distinct sub-varieties, which bore blue and round, white
and round, blue and wrinkled, and white and wrinkled peas; and although
he sowed these four varieties separately during several successive
years, each kind always reproduced all four kinds mixed together!
With respect to the varieties not naturally intercrossing, I have
ascertained that the pea, which in this respect differs from some other
Leguminosae, is perfectly fertile without the aid of insects. Yet I have
seen humble-bees whilst sucking the nectar depress the keel-petals, and
become so thickly dusted with pollen, that some could hardly fail to be
left on the stigma of the next flower which was visited. I have made
inquiries from several great raisers of seed-peas, and I find that but
few sow them separately; the majority take no precaution; and it is
certain, as I have myself found, that true seed may be saved during at
least several generations from distinct varieties growing close
together.[603] Under these circumstances, Mr. Fitch raised, as he
informs me, one variety for twenty {330} years, which always came true.
From the analogy of kidney-beans I should have expected[604] that
occasionally, perhaps at long intervals of time, when some slight
degree of sterility had supervened from long-continued
self-fertilisation, varieties thus growing near each other would have
crossed; and I shall give in the eleventh chapter two cases of distinct
varieties which spontaneously intercrossed, as shown (in a manner
hereafter to be explained) by the pollen of the one variety having
acted directly on the seeds of the other. Whether the incessant supply
of new varieties is partly due to such occasional and accidental
crosses, and their fleeting existence to changes of fashion; or again,
whether the varieties which arise after a long course of continued
self-fertilisation are weakly and soon perish, I cannot even
conjecture. It may, however, be noticed that several of Andrew Knight's
varieties, which have endured longer than most kinds, were raised
towards the close of the last century by artificial crosses; some of
them, I believe, were still, in 1860, vigorous; but now, in 1865, a
writer, speaking[605] of Knight's four kinds of marrows, says, they
have acquired a famous history, but their glory has departed.
With respect to Beans (_Faba vulgaris_), I will say but little. Dr.
Alefeld has given[606] short diagnostic characters of forty varieties.
Every one who has seen a collection must have been struck with the
great difference in shape, thickness, proportional length and breadth,
colour, and size which beans present. What a contrast between a Windsor
and Horse-bean! As in the case of the pea, our existing varieties were
preceded during the Bronze age in Switzerland by a peculiar and now
extinct variety producing very small beans.[607]
_Potato (Solanum tuberosum)._--There is little doubt about the
parentage of this plant; for the cultivated varieties differ extremely
little in general appearance from the wild species, which can be
recognised in its native land at the first glance.[608] The varieties
cultivated in Britain are numerous; thus Lawson[609] gives a
description of 175 kinds. I planted eighteen kinds in adjoining rows;
their stems and leaves differed but little, and in several cases there
was as great an amount of difference between the individuals of the
same variety as between the different varieties. The flowers vary in
size, and in colour between white and purple, but in no other respect,
except that in one kind the sepals were somewhat elongated. One strange
variety has been described which always produces two sorts of flowers,
the first double and sterile, the second single and fertile.[610] The
fruit or berries also differ, but only in a slight degree.[611]
{331}
The tubers, on the other hand, present a wonderful amount of diversity.
This fact accords with the principle that the valuable and selected
parts of all cultivated productions present the greatest amount of
modification. They differ much in size and shape, being globular, oval,
flattened, kidney-like, or cylindrical. One variety from Peru is
described[612] as being quite straight, and at least six inches in
length, though no thicker than a man's finger. The eyes or buds differ
in form, position, and colour. The manner in which the tubers are
arranged on the so-called roots is different; thus in the
_gurken-kartoffeln_ they form a pyramid with the apex downwards, and in
another variety they bury themselves deep in the ground. The roots
themselves run either near the surface or deep in the ground. The
tubers also differ in smoothness and colour, being externally white,
red, purple, or almost black, and internally white, yellow, or almost
black. They differ in flavour and quality, being either waxy or mealy;
in their period of maturity, and in their capacity for long
preservation.
As with many other plants which have been long propagated by bulbs,
tubers, cuttings, &c., by which means the same individual is exposed
during a length of time to diversified conditions, seedling potatoes
generally display innumerable slight differences. Several varieties,
even when propagated by tubers, are far from constant, as will be seen
in the chapter on Bud-variation. Dr. Anderson[613] procured seed from
an Irish purple potato, which grew far from any other kind, so that it
could not at least in this generation have been crossed, yet the many
seedlings varied in almost every possible respect, so that "scarcely
two plants were exactly alike." Some of the plants which closely
resembled each other above ground, produced extremely dissimilar
tubers; and some tubers which externally could hardly be distinguished,
differed widely in quality when cooked. Even in this case of extreme
variability, the parent-stock had some influence on the progeny, for
the greater number of the seedlings resembled in some degree the parent
Irish potato. Kidney potatoes must be ranked amongst the most highly
cultivated and artificial races; yet their peculiarities can often be
strictly propagated by seed. A great authority, Mr. Rivers,[614] states
that "seedlings from the ash-leaved kidney always bear a strong
resemblance to their parent. Seedlings from the fluke-kidney are still
more remarkable for their adherence to their parent-stock, for, on
closely observing a great number during two seasons, I have not been
able to observe the least difference either in earliness,
productiveness, or in the size or shape of their tubers."
* * * * *
{332}