Recalling the results of the last lecture, we see that the species of
the systematists are not in reality units, though in the ordinary course
of floristic studies they may, as a rule, seem to be so. In some cases
representatives of the same species from different countries or regions,
when compared with one another do not exactly agree. Many species of
ferns afford instances of this rule, and Lindley and other great
systematists have frequently been puzzled by the wide range of
differences between the individuals of a single species.
In other cases the differing forms are observed to grow near each other,
sometimes in neighboring provinces, sometimes in the same locality,
growing and flowering in mixtures of two or three or even more
elementary types. The violets exhibit widespread ancient types, from
which the local species may be taken to have arisen. The common
ancestors of the Whitlow-grasses are probably not to be found [64] among
existing forms, but numerous types are crowded together in the southern
part of central Europe and more thinly scattered elsewhere, even as far
as western Asia. There can be little doubt that their common origin is
to be sought in the center of their geographic distribution.
Numerous other cases exhibit smaller numbers of elementary units within
a systematic species; in fact purely uniform species seem to be
relatively rare. But with small numbers there are of course no
indications to be expected concerning their common origin or the
starting point of their distribution.
It is manifest that these experiences with wild species must find a
parallel among cultivated plants. Of course cultivated plants were
originally wild and must have come under the general law. Hence we may
conclude that when first observed and taken up by man, they must already
have consisted of sundry elementary subspecies. And we may confidently
assert that some must have been rich and others poor in such types.
Granting this state of things as the only probable one, we can easily
imagine what must have been the consequences. If a wild species had been
taken into cultivation only once, the cultivated form would have been a
single elementary [65] type. But it is not very likely that such
partiality would occur often. The conception that different tribes at
different times and in distant countries would have used the wild plants
of their native regions seems far more natural than that all should have
obtained plants for cultivation from the same source or locality. If
this theory may be relied upon, the origin of many of the more widely
cultivated agricultural plants must have been multiple, and the number
of the original elementary species of the cultivated types must have
been so much the larger, the more widely distributed and variable the
plants under consideration were before the first period of cultivation.
Further it would seem only natural to explain the wide variability of
many of our larger agricultural and horticultural stocks by such an
incipient multiformity of the species themselves. Through commercial
intercourse the various types might have become mixed so as to make it
quite impossible to point out the native localities for each of them.
Unfortunately historical evidence on this point is almost wholly
lacking. The differences in question could not have been appreciated at
that remote period, and interest the common observer but little even
today. The history of most of the cultivated plants is very obscure,
[66] and even the most skillful historians, by sifting the evidence
afforded by the older writers, and that obtained by comparative
linguistic investigations have been able to do little more than frame
the most general outline of the cultural history of the most common and
most widely used plants.
Some authors assume that cultivation itself might have been the
principal cause of variability, but it is not proved, nor even probable,
that cultivated plants are intrinsically more variable than their wild
prototypes. Appearances in this case are very deceptive. Of course
widely distributed plants are as a rule richer in subspecies than forms
with limited distribution, and the former must have had a better chance
to be taken into cultivation than the latter. In many cases, especially
with the more recent cultivated species, man has deliberately chosen
variable forms, because of their greater promise. Thirdly, wide
variability is the most efficient means of acclimatization, and only
species with many elementary units would have offered the adequate
material for introduction into new countries.
From this discussion it would seem that it is more reasonable to assert
that variability is one of the causes of the success of cultivation,
than to assume that cultivation is a cause of variability [67] at large.
And this assumption would be equally sufficient to explain the existing
conditions among cultivated plants.
Of course I do not pretend to say that cultivated plants should be
expected to be less variable than in the wild state, or that swarms of
elementary species might not be produced during cultivation quite as
well as before. However the chance of such an event, as is easily seen,
cannot be very great, and we shall have to be content with a few
examples of which the coconut is a notable one.
Leaving this general discussion of the subject, we may take up the
example of the beets. The sugar-beet is only one type from among a horde
of others, and though the origin of all the single types is not
historically known, the plant is frequently found in the wild state even
at the present time, and the native types may be compared with the
corresponding cultivated varieties.
The cultivation of beets for sugar is not of very ancient date. The
Romans knew the beets and used them as vegetables, both the roots and
the leaves. They distinguished a variety with white and one with red
flesh, but whether they cultivated them, or only collected them from
where they grew spontaneously, appears to be unknown.
[68] Beets are even now found in large quantities along the shores of
Italy. They prefer the vicinity of the sea, as do so many other members
of the beet family, and are not limited to Italy, but are found growing
elsewhere on the littoral of the Mediterranean, in the Canary Islands
and through Persia and Babylonia to India. In most of their native
localities they occur in great abundance.
The color of the foliage and the size of the roots are extremely
variable. Some have red leafstalks and veins, others a uniform red or
green foliage, some have red or white or yellow roots, or exhibit
alternating rings of a red and of a white tinge on cut surfaces. It
seems only natural to consider the white and the red, and even the
variegated types as distinct varieties, which in nature do not
transgress their limits nor change into one another. In a subsequent
lecture I will show that this at least is the rule with the
corresponding color-varieties in other genera.
The fleshiness or pulpiness of the roots is still more variable. Some
are as thick as the arm and edible, others are not thicker than a finger
and of a woody composition, and the structure of this woody variety is
very interesting. The sugar-beet consists, as is generally known, of
concentric layers of sugar-tissue and of vascular [69] strands; the
larger the first and the smaller the latter, the greater is, as a rule,
the average amount of sugar of the race. Through the kindness of the
late Mr. Rimpau, a well known German breeder of sugar-beet varieties, I
obtained specimens from seed of a native wild locality near Bukharest.
The plants produced quite woody roots, showing almost no sugar tissue at
all. Woody layers of strongly developed fibrovascular strands were seen
to be separated one from another only by very thin layers of
parenchymatous cells. Even the number of layers is variable; it was
observed to be five in my plants; but in larger roots double this number
and even more may easily be met with.
Some authors have distinguished specific types among these wild forms.
While the cultivated beets are collected under the head of _Beta
vulgaris_, separate types with more or less woody roots have been
described as _Beta maritima_ and _Beta patula_. These show differences
in the habit of the stems and the foliage. Some have a strong tendency
to become annual, others to become biennial. The first of course do not
store a large quantity of food in their roots, and remain thin, even at
the time of flowering. The biennial types occur in all sizes of roots.
In the annuals the stems may vary from [70] erect to ascending, and the
name _patula_ indicates stems which are densely branching from the base
with widely spreading branches throughout. Mr. Em. von Proskowetz of
Kwassitz, Austria, kindly sent me seeds of this _Beta patula_, the
variability of which was so great in my cultures as to range from nearly
typical sugar-beets to the thin woody type of Bukharest.
Broad and narrow leaves are considered to be differentiating marks
between _Beta vulgaris_ and _Beta patula_, but even here a wide range of
forms seem to occur.
Rimpau, Proskowetz, Schindler and others have made cultures of beets
from wild localities in order to discover a hypothetical common ancestor
of all the present cultivated types. These researches point to the _B.
patula_ as the probable ancestor, but of course they were not made to
decide the question as to whether the origination of the several now
existing types had taken place before or during culture. From a general
point of view the variability of the wild species is parallel to that of
the cultivated forms to such a degree as to suggest the multiple origin
of the former. But a close investigation of this highly important
problem has still to be made.
The varieties of the cultivated beets are commonly [71] included in four
subspecies. The two smallest are the salad-beets and the ornamental
forms, the first being used as food, and ordinarily cultivated in red
varieties, the second being used as ornamental plants during the fall,
when they fill the beds left empty by summer flowers, with a bright
foliage that is exceedingly rich in form and color. Of the remaining
subspecies, one comprises the numerous sorts cultivated as forage-crops
and the other the true sugar-beets. Both of them vary widely as to the
shape and the size of the roots, the quality of the tissue, the foliage
and other characteristics.
Some of these forms, no doubt, have originated during culture. Most of
them have been improved by selection, and no beet found in the wild
state ever rivals any cultivated variety. But the improvement chiefly
affects the size, the amount of sugar and nutrient substances and some
other qualities which recur in most of the varieties. The varietal
attributes themselves however, are more or less of a specific nature,
and have no relation to the real industrial value of the race. The
short-rooted and the horn-shaped varieties might best be cited as
examples.
The assertion that the sundry varieties of forage-beets are not the
result of artificial selection, [72] is supported in a large measure by
the historic fact that the most of them are far older than the method of
conscious selection of plants itself. This method is due to Louis
Vilmorin and dates from the middle of the last century. But in the
sixteenth century most of our present varieties of beets were already in
cultivation. Caspar Bauhin gives a list of the beets of his time and it
is not difficult to recognize in it a large series of subspecies and
varieties and even of special forms, which are still cultivated. A more
complete list was published towards the close of the same century by
Olivier de Serres in his world-renowned "Theatre d'Agriculture" (Paris,
1600).
The red forage-beets which are now cultivated on so large a scale, had
been introduced from Italy into France only a short time before.
From this historic evidence, the period during which the beets were
cultivated from the time of the Romans or perhaps much later, up to the
time of Bauhin and De Serres, would seem far too short for the
production by the unguided selection of man of all the now existing
types. On the other hand, the parallelism between the characters of some
wild and some cultivated varieties goes to make it very probable that
other varieties have been found in the same way, some in this country
and others in that, [73] and have been taken into cultivation
separately. Afterwards of course all must have been improved in the
direction required by the needs of man.
Quite the same conclusion is afforded by apples. The facts are to some
extent of another character, and the rule of the derivation of the
present cultivated varieties from original wild forms can be illustrated
in this case in a more direct way. Of course we must limit ourselves to
the varieties of pure ancestry and leave aside all those which are of
hybrid or presumably hybrid origin.
Before considering their present state of culture, something must be,
said about the earlier history and the wild state of the apples.
The apple-tree is a common shrub in woods throughout all parts of
Europe, with the only exception of the extreme north. Its distribution
extends to Anatolia, the Caucasus and Ghilan in Persia. It is found in
nearly all forests of any extent and often in relatively large numbers
of individuals. It exhibits varietal characters, which have led to the
recognition of several spontaneous forms, especially in France and in
Germany.
The differentiating qualities relate to the shape and indumentum of the
leaves. Nothing is known botanically as to differences between [74] the
fruits of these varieties, but as a matter of fact the wild apples of
different countries are not at all the same.
Alphonse De Candolle, who made a profound study of the probable origin
of most of our cultivated plants, comes to the conclusion that the apple
tree must have had this wide distribution in prehistoric times, and that
its cultivation began in ancient times everywhere.
This very important conclusion by so high an authority throws
considerable light on the relation between cultivated and wild varieties
at large. If the historic facts go to prove a multiple origin for the
cultivation of some of the more important useful plants, the probability
that different varieties or elementary species have been the starting
points for different lines of culture, evidently becomes stronger.
Unfortunately, this historic evidence is scanty. The most interesting
facts are those concerning the use of apples by the Romans and by their
contemporaries of the Swiss and middle European lake-dwellings. Oswald
Heer has collected large numbers of the relics of this prehistoric
period. Apples were found in large quantities, ordinarily cut into
halves and with the signs of having been dried. Heer distinguished two
varieties, one with large and one with small fruits. The first about 3
and [75] the other about 1.5-2 cm. in diameter. Both are therefore very
small compared with our present ordinary varieties, but of the same
general size as the wild forms of the present day. Like these, they must
have been of a more woody and less fleshy tissue. They would scarcely
have been tasteful to us, but in ancient times no better varieties were
known and therefore no comparison was possible.
There is no evidence concerning the question, as to whether during the
periods mentioned apples were cultivated or only collected in the wild
state. The very large numbers which are found, have induced some writers
to believe in their culture, but then there is no reason why they should
not have been collected in quantity from wild shrubs. The main fact is
that the apple was not a uniform species in prehistoric times but showed
even then at least some amount of variability.
At the present day the wild apples are very rich in elementary species.
Those of Versailles are not the same as those of Belgium, and still
others are growing in England and in Germany. The botanical differences
derived from the blossoms and the leaves are slight, but the flavor,
size and shape of the fruits diverge widely. Two opinions have been
advanced to explain this high degree of variability, but [76] neither of
them conveys a real explanation; their aim is chiefly to support
different views as to the causes of variability, and the origin of
elementary species at large.
One opinion, advocated by De Candolle, Darwin and others, claims that
the varieties owe their origin to the direct influence of cultivation,
and that the corresponding forms found in the wild state, are not at all
original, but have escaped from cultivation and apparently become wild.
Of course this possibility cannot be denied, at least in any single
instance, but it seems too sweeping an assertion to make for the whole
range of observed forms.
The alternative theory is that of van Mons, the Belgian originator of
commercial varieties of apples, who has published his experiments in a
large work called "Arbres fruitiers ou Pomonomie belge." Most of the
more remarkable apples of the first half of the last century were
produced by van Mons, but his greatest merit is not the direct
production of a number of good varieties, but the foundation of the
method, by which new varieties may be obtained and improved.
According to van Mons, the production of a new variety consists chiefly
of two parts. The first is the discovery of a subspecies with new
desirable qualities. The second is the transformation [77] of the
original small and woody apple into a large, fleshy and palatable
variety. Subspecies, or what we now call elementary species were not
produced by man; nature alone creates new forms, as van Mons has it. He
examined with great care the wild apples of his country, and especially
those of the Ardennes, and found among them a number of species with
different flavors. For the flavor is the one great point, which must be
found ready in nature and which may be improved, but can never be
created by artificial selection. The numerous differences in flavor are
quite original; all of them may be found in the wild state and most of
them even in so limited a region as the Ardennes Mountains. Of course
van Mons preferred not to start from the wild types themselves, when the
same flavor could be met with in some cultivated variety. His general
method was, to search for a new flavor and to try to bring the bearer of
it up to the desired standard of size and edibility.
The latter improvement, though it always makes the impression of an
achievement, is only the last stone to be added to the building up of
the commercial value of the variety. Without it, the best flavored apple
remains a crab; with it, it becomes a conquest. According to the method
of van Mons it may be reached within [78] two or three generations, and
a man's life is wholly sufficient to produce in this way many new types
of the very best sorts, as van Mons himself has done. It is done in the
usual way, sowing on a large scale and selecting the best, which are in
their turn brought to an early maturation of their fruit by grafting,
because thereby the life from seed to seed may be reduced to a few
years.
Form, taste, color, flavor and other valuable marks of new varieties are
the products of nature, says van Mons, only texture, fleshiness and size
are added by man. And this is done in each new variety by the same
method and according to the same laws. The richness of the cultivated
apples of the present day was already present in the large range of
original wild elementary species, though unobserved and requiring
improvement.
An interesting proof of this principle is afforded by the experience of
Mr. Peter M. Gideon, as related by Bailey. Gideon sowed large quantities
of apple-seeds, and one seed produced a new and valuable variety called
by him the "Wealthy" apple. He first planted a bushel of apple-seeds,
and then every year, for nine years, planted enough seeds to produce a
thousand trees. At the end of ten years all seedlings had perished
except one hardy seedling [79] crab. This experiment was made in
Minnesota, and failed wholly. Then he bought a small lot of seeds of
apples and crab-apples in Maine and from these the "Wealthy" came. There
were only about fifty seeds in the lot of crab-apple seed which produced
the "Wealthy," but before this variety was obtained, more than a bushel
of seed had been sown. Chance afforded a species with an unknown taste;
but the growing of many thousands of seedlings of known varieties was
not the best means to get something really new.
Pears are more difficult to improve than apples. They often require six
or more generations to be brought from the wild woody state to the
ordinary edible condition. But the varieties each seem to have a
separate origin, as with apples, and the wide range of form and of taste
must have been present in the wild state, long before cultivation. Only
recently has the improvement of cherries, plums, currants and
gooseberries been undertaken with success by Mr. Burbank, and the
difference between the wild and cultivated forms has hitherto been very
small. All indications point to the existence, before the era of
cultivation, of larger or smaller numbers of elementary species.
The same holds good with many of the larger forage crops and other
plants of great industrial [80] value. Clover exhibits many varieties,
which have been cultivated indiscriminately, and often in motley
mixtures. The flower heads may be red or white, large or small,
cylindric or rounded, the leaves are broader or narrower, with or
without white spots of a curious pattern. They may be more or less hairy
and so forth. Even the seeds exhibit differences in size, shape or
color, and of late Martinet has shown, that by the simple means of
picking out seeds of the same pattern, pure strains of clover may be
obtained, which are of varying cultural value. In this way the best
subspecies or varieties may be sought out for separate cultivation. Even
the white spots on the leaflets have proved to be constant characters
corresponding with noticeable differences in yield.
Flax is another instance. It was already cultivated, or at least made
use of during the period of the lake-dwellers, but at that time it was a
species referred to as _Linum angustifolium_, and not the _Linum
usitatissimum_, which is our present day flax. There are now many
subspecies, elementary species, and varieties under cultivation. The
oldest of them is known as the "springing flax," in opposition to the
ordinary "threshing flax." It has capsules which open of themselves, in
order to disseminate the seeds, while the ordinary heads of the [81]
flax remain closed until the seeds are liberated by threshing. It seems
probable that the first form or _Linum crepitans_ might thrive in the
wild state as well as any other plant, while in the common species those
qualities are lacking which are required for a normal dissemination of
the seeds. White or blue flowers, high or dwarf stems, more or less
branching at the base and sundry other qualities distinguish the
varieties, aside from the special industrial difference of the fibres.
Even the life-history varies from annual and biennial, to perennial.
It would take us too long to consider other instances. It is well known
that corn, though considered as a single botanical species, is
represented by different subspecies and varieties in nearly every region
in which it is grown. Of course its history is unknown and it is
impossible to decide whether all the tall and dwarf forms, or starchy
and sweet varieties, dented or rounded kernels, and hundreds of others
are older than culture or have come into existence during historic
times, or as some assume, through the agency of man. But our main point
now is not the origin, but only the existence of constant and sharply
differentiated forms within botanical species. Nearly every cultivated
plant affords instances of such diversity. Some include a few types
only, while [82] others show, a large number of forms clearly separated
to a greater or lesser degree.
In some few instances it is obvious that this variability is of later
date than culture. The most conspicuous case is that of the coconut.
This valuable palm is found on nearly all tropical coasts, in America,
as well as in Asia, but in Africa and Australia there are many hundreds
of miles of shore line, where it is not found. Its importance is not at
all the same everywhere. On the shores and islands of the Indian Ocean
and the Malay Archipelago, man is chiefly dependent upon it, but in
America it is only of subordinate usefulness.
In connection with these facts, it abounds in subspecies and varieties
in the East Indian regions, but on the continent of America little
attention has as yet been given to its diverging qualities. In the
Malayan region it affords nearly all that is required by the
inhabitants. The value of its fruit as food, and the delicious beverage
which it yields, are well known. The fibrous rind is not less useful; it
is manufactured into a kind of cordage, mats and floor-cloths. An
excellent oil is obtained from the kernel by compression. The hard
covering of the stem is converted into drums and used in the
construction of huts; the lower part is so hard as to take on a
beautiful polish [83] when it resembles agate. Finally the unexpanded
terminal bud is a delicate article of food. Many other uses could be
mentioned, but these may suffice to indicate how closely the life of the
inhabitants is bound up with the culture of this palm, and how sharply,
in consequence, its qualities must have been watched by early man. Any
divergence from the ordinary type must have been noted; those which were
injurious must have been rejected, but the useful ones must have been
appreciated and propagated. In a word any degree of variability afforded
by nature must have been noticed and cultivated.
More than fifty different sorts of the coconut are described from the
Indian shores and islands, with distinct local and botanical names.
Miquel, who was one of the best systematists of tropical plants, of the
last century, described a large number of them, and since, more have
been added. Nearly all useful qualities vary in a higher or lesser
degree in the different varieties. The fibrous strands of the rind of
the nut are developed in some forms to such a length and strength as to
yield the industrial product known as the coir-fibre. Only three of them
are mentioned by Miquel that have this quality, the _Cocos nucifera
rutila_, _cupuliformis_ and _stupposa_. Among them the _rutila_ [84]
yields the best and most supple fibres, while those of the _stupposa_
are stiff and almost unbending.
The varieties also differ greatly in size, color, shape and quality, and
the trees have also peculiar characteristics. One variety exhibits
leaves which are nearly entire, the divisions being only imperfectly
separated, as often occurs in the very first leaves of the seedlings of
other varieties. The flavor of the flesh, oil and milk likewise yield
many good varietal marks.
In short, the coconut-palm comes under the general rule, that botanical
species are built up of a number of sharply distinguishable types, which
prove their constancy and relative independence by their wide
distribution in culture. In systematic works all these forms are called
varieties, and a closer investigation of their real systematic value has
not yet been made. But the question as to the origin of the varieties
and of the coconut itself has engrossed the attention of many botanists,
among whom are De Candolle in the middle of the last century, and Cook
at its close.
Both questions are closely connected. De Candolle claimed an Asiatic
origin for the whole species, while Cook's studies go to prove that its
original habitat is to be sought in the northern countries of South
America. Numerous [85] varieties are growing in Asia and have as yet not
been observed to occur in America, where the coconut is only of
subordinate importance, being one of many useful plants, and not the
only one relied upon by the natives for their subsistence. If therefore,
De Candolle's opinion is the right one, the question as to whether the
varieties are older or younger than the cultivated forms of the species,
must always remain obscure. But if the proofs of an American origin
should be forthcoming, the possibility, and even the probability that
the varieties are of later date than the beginning of their culture, and
have originated while in this condition must at once be granted. An
important point in the controversy is the manner in which the coconuts
were disseminated from shore to shore, from island to island. De
Candolle, Darwin and most of the European writers claim that the
dispersal was by natural agencies, such as ocean-currents. They point
out that the fibrous rind or husk would keep the fruits afloat, and
uninjured, for many days or even many weeks, while being carried from
one country to another in a manner that would explain their geographic
distribution. But the probability of the nuts being thrown upon the
strand, and far enough from the shore to find suitable conditions for
their germination, is a very small one. To insure [86] healthy and
vigorous seedlings the nuts must be fully ripe, after which planting
cannot be safely delayed for more than a few weeks. If kept too moist
the nuts rot. If once on the shore, and allowed to lie in the sun, they
become overheated and are thereby destroyed; if thrown in the shade of
other shrubs and trees, the seedlings do not find the required
conditions for a vigorous growth.
Some authors have taken the fibrous rind to be especially adapted to
transport by sea, but if this were so, this would argue that water is
the normal or at least the very frequent medium of dissemination, which
of course it is not. We may, claim with quite as much right that the
thick husk is necessary to enable the heavy fruit to drop from tall
trees with safety. But even for this purpose the protection is not
sufficient, as the nuts often suffer from falling to such a degree as to
be badly injured as to their germinating qualities. It is well known
that nuts, which are destined for propagation, are as a rule not allowed
to fall off, but are taken from the trees with great care.
Summing up his arguments, Cook concludes that there is little in the way
of known facts to support the poetic theory of the coconut palm dropping
its fruits into the sea to float away to barren islands and prepare them
for [87] human habitation. Shipwrecks might furnish a successful method
of launching viable coconuts, and such have no doubt sometimes
contributed to their distribution. But this assumption implies a
dissemination of the nuts by man, and if this principal fact is granted,
it is far more natural to believe in a conscious intelligent
dissemination.
The coconut is a cultivated tree. It may be met with in some spots
distant from human dwellings, but whenever such cases have been
subjected to a closer scrutiny, it appears that evidently, or at least
probably, huts had formerly existed in their neighborhood, but having
been destroyed by some accident, had left the palm trees uninjured. Even
in South America, where it may be found in forests at great distances
from the sea-shore, it is not at all certain that true native localities
occur, and it seems to be quite lost in its natural condition.
Granting the cultivated state of the palms as the only really important
one, and considering the impossibility or at least great improbability
of its dissemination by natural means, the distribution by man himself,
according to his wants, assumes the rank of an hypothesis fully adequate
to the explanation of all the facts concerning the life-history of the
tree.
We now have to inquire into the main question, [88] whether it is
probable that the coconut is of American or of Asiatic origin, leaving
aside the historic evidence which goes to prove that nothing is known
about the period in which its dissemination from one hemisphere to
another took place, we will now consider only the botanic and geographic
evidence, brought forward by Cook. He states that the whole family of
coconut-palms, consisting of about 20 genera and 200 species, are all
strictly American with the exception of the rather aberrant African
oilpalm, which has, however, an American relative referred to the same
genus. The coconut is the sole representative of this group which is
connected with Asia and the Malayan region, but there is no manifest
reason why other members of the same group could not have established
themselves there, and maintained an existence under conditions, which
are not at all unfavorable to them. The only obvious reason is the
assumption already made, that the distribution was brought about by man,
and thus only affected the species, chosen by him for cultivation. That
the coconut cannot have been imported from Asia into America seems to be
the most obvious conclusion from the arguments given. It should be
briefly noted, that it was known and widely distributed in tropical
America at the time of the discovery of that continent [89] by Columbus,
according to accounts of Oviedo and other contemporary Spanish writers.
Concluding we may state that according to the whole evidence as it has
been discussed by De Candolle and especially by Cook, the coconut-palm
is of American origin and has been distributed as a cultivated tree by
man through the whole of its wide range. This must have happened in a
prehistoric era, thus affording time enough for the subsequent
development of the fifty and more known varieties. But the possibility
that at least some of them have originated before culture and have been
deliberately chosen by man for distribution, of course remains
unsettled.
Coconuts are not very well adapted for natural dispersal on land, and
this would rather induce us to suppose an origin within the period of
cultivation for the whole group. There are a large number of cultivated
varieties of different species which by some peculiarity do not seem
adapted for the conditions of life in the wild state. These last have
often been used to prove the origin of varietal forms during culture.
One of the oldest instances is the variety or rather subspecies of the
opium-poppy, which lacks the ability to burst open its capsules. The
seeds, which are thrown out by the wind, in the common forms, through
the apertures underneath [90] the stigma, remain enclosed. This is
manifestly a very useful adaptation for a cultivated plant, as by this
means no seeds are lost. It would be quite a disadvantage for a wild
species, and is therefore claimed to have been connected from the
beginning with the cultivated form.
The large kernels of corn and grain, of beans and peas, and even of the
lupines were considered by Darwin and others to be unable to cope with
natural conditions of life. Many valuable fruits are quite sterile, or
produce extremely few seeds. This is notoriously the case with some of
the best pears and grapes, with the pine-apples, bananas, bread-fruits,
pomegranate and some members of the orange tribe. It is open to
discussion as to what may be the immediate cause of this sterility, but
it is quite evident, that all such sterile varieties must have
originated in a cultivated condition. Otherwise they would surely have
been lost.
In horticulture and agriculture the fact that new varieties arise from
time to time is beyond all doubt, and it is not this question with which
we are now concerned. Our arguments were only intended to prove that
cultivated species, as a rule, are derived from wild species, which obey
the laws discussed in a previous lecture. The botanic units are compound
entities, and [91] the real systematic units in elementary species play
the same part as in ordinary wild species. The inference that the origin
of the cultivated plants is multiple, in most cases, and that more than
one, often many separate elementary forms of the same species must
originally have been taken into cultivation, throws much light upon many
highly important problems of cultivation and selection. This aspect of
the question will therefore be the subject of the next lecture.
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