Wheat quickly a.s.sumes new habits of life. The summer and winter kinds were cla.s.sed by Linnaeus as distinct species; but M. Monnier (9/37. Quoted by G.o.dron "De l"Espece" volume 2 page 74. So it is, according to Metzger "Getreidearten" s. 18, with summer and winter barley.) 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 (9/38. Loiseleur-Deslongchamps "Cereales" part 2 page 224. Le Couteur page 70. Many other accounts could be added.) differently from our European varieties. In Canada the first settlers, according to Kalm (9/39. "Travels in North America" 1753-1761 English translation volume 3 page 165.), found their winters too severe for winter-wheat brought from France, and their summers often too short for summer-wheat; and they thought that their country was useless for corn crops until they procured summer-wheat from the northern parts of Europe, which succeeded well. 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 (9/40. "Cereales" part 2 pages 179-183.) 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 (9/41. "On the Varieties of Wheat" Introduction page 7. See Marshall "Rural Econ. of Yorkshire" volume 2 page 9. With respect to similar cases of adaptation in the varieties of oats see some interesting papers in the "Gardener"s Chronicle and Agricult. Gazette" 1850 pages 204, 219.) 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 hardness, 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 (9/42. "On the Varieties of Wheat" page 59. Mr. Shirreff and a higher authority cannot be given ("Gardener"s Chronicle and Agricult.
Gazette" 1862 page 963), says "I have never seen grain which has either been improved or degenerated by cultivation, so as to convey the change to the succeeding crop.), 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 observation 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 pa.s.sed 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 Tritic.u.m originally existed in nearly the same condition as at present, rest their belief chiefly on the great antiquity of the several forms. (9/43. Alph. De Candolle "Geograph. Bot." page 930. ) It is an important fact, which we have recently learnt from the admirable researches of Heer (9/44. "Pflanzen der Pfahlbauten" 1866.), 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 panic.u.m, 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 Neolithic period, had already made considerable progress; for, besides the 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 panic.u.m 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 (9/45. "Les Cereales" page 94.) has argued that, if our cereal plants have 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 p.r.o.nounced variations appear, which, as Mr. Shirreff 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 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 (9/46. Quoted by Le Couteur page 16.) 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 has been found by Le Coutour and Hallett. Although the principle of selection is so important, yet the little which man has effected, by incessant efforts (9/47. A. De Candolle "Geograph. Bot." page 932.) 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 quant.i.ty 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 civilised 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 cla.s.s 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. (9/48. O. Heer "Die Pflanzen der Pfahlbauten" 1866.
The following pa.s.sage is quoted from Dr. Christ in "Die Fauna der Pfahlbauten, von Dr. Rutimeyer" 1861 s. 225.) "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 were "smaller, shorter, and nearer to each other, than in that now grown; without the husk they were 2 1/2 lines long, and scarcely 1 1/2 broad, whilst those now grown have a length of three lines, and almost the same in breadth." (9/49. Heer as quoted by Carl Vogt "Lectures on Man" English translation page 355.) 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. dicocc.u.m) differs from all known varieties of this form. A fifth kind (T. monococc.u.m) 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 descriptions given by palaeontologists of the first appearance, the increasing rarity, and final extinction or modification of fossil species, embedded in the successive stages of a geological formation.
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 OR INDIAN CORN: Zea mays.
Botanists are nearly unanimous that all the cultivated kinds belong to the same species. It is undoubtedly (9/50. See Alph. De Candolle"s long discussion in his "Geograph. Bot." page 942. With respect to New England see Silliman"s "American Journal" volume 44 page 99.) 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 (9/51. "Travels in Peru" English translation page 177.) 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 (9/52. "Geolog.
Observ. on S. America" 1846 page 49.) heads of maize, together with eighteen species of recent sea-sh.e.l.l, 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 (9/53. This maize is figured in Bonafous" magnificent work, "Hist. Nat. du Mais" 1836 P1. v. bis, and in the "Journal of Hort. Soc."
volume 1 1846 page 115 where an account is given of the result of sowing the seed. A young Guarany Indian, on seeing this kind of maize, told Auguste St. Hilaire (see De Candolle "Geograph. Bot." page 951) that it grew wild in the humid forests of his native land. Mr. Teschemacher in "Proc. Boston Soc. Hist." October 19, 1842 gives an account of sowing the seed.), in which the grains, instead of being naked, are concealed by husks as much as eleven lines in length, has been stated, but on insufficient evidence, to grow wild in Brazil. It is almost certain that the aboriginal form would have had its grains thus protected (9/54. Moquin-Tandon "Elements de Teratologie" 1841 page 126.); 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 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 (9/55.
"Die Getreidearten" 1841 s. 208. I have modified a few of Metzger"s statements in accordance with those made by Bonafous in his great work "Hist. Nat. du Mais" 1836.), 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 (9/56. G.o.dron "De l"Espece"
tome 2 page 80; Al. De Candolle ibid page 951.); 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, and which is extensively cultivated in the United States as sweet corn) 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. (9/57. "Transact. Bot.
Soc. of Edinburgh" volume 8 page 60.) Azara describes (9/58. "Voyages dans l"Amerique Meridionale" tome 1 page 147.) 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. (9/59. Bonafous "Hist. Nat. du Mais" page 31.) 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 a.s.sumed a yellow colour. But Bonafous (9/60. Ibid page 31.) 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 lat.i.tudes, 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 three to four months. (9/61. Metzger "Getreidearten" s. 206.) Peter Kalm (9/62.
"Description of Maize" by P. Kalm 1752 in "Swedish Acts" volume 4. I have consulted an old English MS. translation.), 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. 43-44 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. 45-47 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 a.n.a.logous 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 seeds 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 (9/63. "Getreidearten" s. 208.) in one case, namely, with a tall kind (Breit-korniger mais, Zea altissima) brought from the warmer parts of America. During the first year the plants were twelve feet high, and a 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. a.n.a.logous 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. In the above cases the seeds were carried from a warm to a colder climate. But Fritz Muller informs me that a dwarf variety with small rounded seeds (papa-gaien-mais), introduced from Germany into S. Brazil, produces plants as tall, with seeds as flat, as those of the kind commonly cultivated there.]
These facts afford the most remarkable instance known to me of the direct and prompt action of climate on a plant. It might 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 (Bra.s.sica 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 (9/64. "Cabbage Timber" "Gardener"s Chronicle" 1856 page 744, quoted from Hooker "Journal of Botany." A walking-stick made from a cabbage-stalk is exhibited in the Museum at Kew.) 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 kails, 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 which are valued solely for ornament. 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 ma.s.ses above the ground; and the recently formed new race (9/65. "Journal de la Soc. Imp. d"Horticulture" 1855 page 254 quoted from "Gartenflora" April 1855.) of the 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. (9/66. G.o.dron "De l"Espece" tome 2 page 52; Metzger "Syst. Beschreibung der Kult. Kohlarten" 1833 s. 6.) I compared the flowers of all the princ.i.p.al 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, 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 ma.s.s, 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. (9/67. Regnier "De l"Economie Publique des Celtes" 1818 page 438.)
It would be useless to give a cla.s.sified description (9/68. See the elder De Candolle in "Transact. of Hort. Soc." volume 5; and Metzger "Kohlarten"
etc.) of the numerous races, sub-races, and varieties of the cabbage; but it may be mentioned that Dr. Lindley has lately proposed (9/69. "Gardener"s Chronicle" 1859 page 992.) a system founded on the state of development of the terminal and lateral leaf-buds. Thus:
I. All the leaf-buds active and open, as in the wild-cabbage, kail, etc.
II. All the leaf-buds active, but forming heads, as in Brussel-sprouts, etc.
III. Terminal leaf-bud alone active, forming a head as in common cabbages, savoys, etc.
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 princ.i.p.al kinds of cabbage existed at least as early as the sixteenth century (9/70. Alph. De Candolle "Geograph. Bot." pages 842 and 989.), 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 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 mongrelised; 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 Kail," has lately been produced by crossing common kail and Brussel- sprouts, recrossed with purple broccoli (9/71. "Gardener"s Chronicle"
February 1858 page 128.), and is said to be true; but plants raised by me were not nearly so constant in character as any common kind of 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 (9/72. "Kohlarten" s. 22.) 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. (9/73. G.o.dron "De l"Espece" tome 2 page 52; Metzger "Kohlarten" s.
22.) 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 sh.o.r.es of Europe; but Alph. De Candolle (9/74.
"Geograph. Bot." page 840.) 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 Bra.s.sica are descended, according to the view adopted by G.o.dron and Metzger (9/75. G.o.dron "De l"Espece" tome 2 page 54; Metzger "Kohlarten" s. 10.), 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. Bra.s.sica napus has given rise to two large groups, namely, Swedish turnips (believed to be of hybrid origin) (9/76. "Gardener"s Chronicle and Agricult. Gazette" 1856 page 729. See more especially ibid 1868 page 275: the writer a.s.serts that he planted a variety of cabbage (B. oleracea) close to turnips (B. rapa) and raised from the crossed seedlings true Swedish turnips. These latter plants ought, therefore, to be cla.s.sed with cabbages or turnips, and not under B. napus.) and Colzas, the seeds of which yield oil. Bra.s.sica 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 G.o.dron 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. (9/77.
"Gardener"s Chronicle and Agricult. Gazette" 1855 page 730.) 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. (9/78. Metzger, "Kohlarten" s. 51.)
In the production of large, fleshy, turnip-like stems, we have a case of a.n.a.logous 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 bow quickly the roots of the wild parsnip can be enlarged, as Vilmorin formerly proved in the case of the carrot. (9/79. These experiments by Vilmorin have been quoted by many writers. An eminent botanist, Prof. Decaisne, has lately expressed doubts on the subject from his own negative results, but these cannot be valued equally with positive results. On the other hand, M. Carriere has lately stated ("Gardener"s Chronicle" 1865 page 1154), that he took seed from a wild carrot, growing far from any cultivated land, and even in the first generation the roots of his seedlings differed in being spindle-shaped, longer, softer, and less fibrous than those of the wild plant. From these seedlings he raised several distinct varieties.)
This latter plant, in its cultivated state, differs in scarcely any character from the wild English carrot, except in general luxuriance and in the size and quality of its roots; but ten varieties, differing in the colour, shape, and quality of the root, are cultivated in England and come true by seed. (9/80. Loudon"s "Encyclop. of Gardening" page 835.) 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, a.n.a.logous modifications have been again and again selected, until at last a great amount of change has been effected.
With respect to the radish, M. Carriere, by sowing the seed of the wild Rapha.n.u.s raphanistrum in rich soil, and by continued selection during several generations, raised many varieties, closely like the cultivated radish (R. sativus) in their roots, as well as the wonderful Chinese variety, R. caudatus: (see "Journal d"Agriculture pratique" tome 1 1869 page 159; also a separate essay "Origine des Plantes Domestiques" 1869.) Rapha.n.u.s raphanistrum and sativus have often been ranked as distinct species, and owing to differences in their fruit even as distinct genera; but Professor Hoffman ("Bot. Zeitung" 1872 page 482) has now shown that these differences, remarkable as they are, graduate away, the fruit of R.
caudatus being intermediate. By cultivating R. raphanistrum during several generations (ibid 1873 page 9), Professor Hoffman also obtained plants bearing fruits like those of R. sativus.
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. (9/81. Alph. De Candolle "Geograph. Bot." 960. Mr. Bentham "Hort. Journal" volume 9 1855 page 141 believes that garden and field peas belong to the same species, and in this respect he differs from Dr. Targioni.) 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. Alefield has recently studied (9/82. "Botanische Zeitung" 1860 s. 204.) the genus with care, and, after having cultivated about fifty varieties, concludes that certainly they all belong to the same species. It is an interesting fact already alluded to, that, according to O. Heer (9/83. "Die Pflanzen der Pfahlbauten" 1866 s. 23.) 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 the field-pea. The varieties of the common garden-pea are numerous, and differ considerably from one another. For comparison I planted at the same time forty-one, English and French varieties. They differed greatly in height,-- namely from between 6 and 12 inches to 8 feet (9/84. A variety called the Rounciva attains this height, as is stated by Mr. Gordon in "Transact.
Hort. Soc." 2nd series volume 1 1835 page 374 from which paper I have taken some facts.),--in manner of growth, and in period of maturity. Some 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:--HAIR"S 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, two, or several flowers in a small cl.u.s.ter, are borne on the same peduncle; and this is a difference which is considered of specific value in some of the Leguminosae. 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 the POIS NAIN HATIF; but HAIR"S 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.