Ent. Soc." ut supra page 317.) that the moths of all kinds vary much in colour, but in nearly the same inconstant manner. Considering how much the coc.o.o.ns in the several races differ, this fact is of interest, and may probably be accounted for on the same principle as the fluctuating variability of colour in the caterpillar, namely, that there has been no motive for selecting and perpetuating any particular variation.
The males of the wild Bombycidae "fly swiftly in the day-time and evening, but the females are usually very sluggish and inactive." (8/77. Stephen"s Ill.u.s.trations, "Haustellata" volume 2 page 35. See also Capt. Hutton "Transact. Ent. Soc." ibid page 152.) In several moths of this family the females have abortive wings, but no instance is known of the males being incapable of flight, for in this case the species could hardly have been perpetuated. In the silk-moth both s.e.xes have imperfect, crumpled wings, and are incapable of flight; but still there is a trace of the characteristic difference in the two s.e.xes; for though, on comparing a number of males and females, I could detect no difference in the development of their wings, yet I was a.s.sured by Mrs. Whitby that the males of the moths bred by her used their wings more than the females, and could flutter downwards, though never upwards. She also states that, when the females first emerge from the coc.o.o.n, their wings are less expanded than those of the male. The degree of imperfection, however, in the wings varies much in different races and under different circ.u.mstances. M. Quatref.a.ges (8/78. "Etudes sur les Maladies du Ver a Soie" 1859 pages 304, 209.) says that he has seen a number of moths with their wings reduced to a third, fourth, or tenth part of their normal dimensions, and even to mere short straight stumps: "il me semble qu"il y a la un veritable arret de developpement partiel." On the other hand, he describes the female moths of the Andre Jean breed as having "leurs ailes larges et etalees. Un seul presente quelques courbures irregulieres et des plis anormaux." As moths and b.u.t.terflies of all kinds reared from wild caterpillars under confinement often have crippled wings, the same cause, whatever it may be, has probably acted on silk-moths, but the disuse of their wings during so many generations has, it may be suspected, likewise come into play.
The moths of many breeds fail to glue their eggs to the surface on which they are laid (8/79. Quatref.a.ges "Etudes" etc. page 214.) but this proceeds, according to Capt. Hutton (8/80. "Transact. Ent. Soc." ut supra page 151.), merely from the glands of the ovipositor being weakened.
As with other long-domesticated animals, the instincts of the silk-moth have suffered. The caterpillars, when placed on a mulberry-tree, often commit the strange mistake of devouring the base of the leaf on which they are feeding, and consequently fall down; but they are capable, according to M. Robinet (8/81. "Manuel de l"Educateur" etc. page 26.) of again crawling up the trunk. Even this capacity sometimes fails, for M. Martins (8/82.
G.o.dron "De l"Espece" page 462.) placed some caterpillars on a tree, and those which fell were not able to remount and perished of hunger; they were even incapable of pa.s.sing from leaf to leaf.
Some of the modifications which the silk-moth has undergone stand in correlation with one another. Thus, the eggs of the moths which produce white coc.o.o.ns and of those which produce yellow coc.o.o.ns differ slightly in tint. The abdominal feet, also, of the caterpillars which yield white coc.o.o.ns are always white, whilst those which give yellow coc.o.o.ns are invariably yellow. (8/83. Quatref.a.ges "Etudes" etc. pages 12, 209, 214.) We have seen that the caterpillars with dark tiger-like stripes produce moths which are more darkly shaded than other moths. It seems well established (8/84. Robinet "Manuel" etc. page 303.) that in France the caterpillars of the races which produce white silk, and certain black caterpillars, have resisted, better than other races, the disease which has recently devastated the silk-districts. Lastly, the races differ const.i.tutionally, for some do not succeed so well under a temperate climate as others; and a damp soil does not equally injure all the races. (8/85. Robinet ibid page 15.)]
From these various facts we learn that silk-moths, like the higher animals, vary greatly under long-continued domestication. We learn also the more important fact that variations may occur at various periods of life, and be inherited at a corresponding period. And finally we see that insects are amenable to the great principle of Selection.
CHAPTER 1.IX.
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 BRa.s.sICA.
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 pa.s.s 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, etc., 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 incidentally given. One chief object in the two following chapters is to show how many characters in our cultivated plants have become variable.
Before entering on details a few general remarks on the origin of cultivated plants may be introduced. M. Alph. De Candolle (9/1. "Geographie botanique raisonnee" 1855 pages 810 to 991.) 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 (9/2. Review by Mr. Bentham in "Hort. Journal" volume 9 1855 page 133 ent.i.tled "Historical Notes on cultivated Plants" by Dr. A.
Targioni-Tozzetti. See also "Edinburgh Review" 1866 page 510.) 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, capsic.u.m, 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 (9/3. "Hist. Notes" as above by Targioni-Tozzetti.) 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. The difficulty would also be removed if they have been exterminated during the progress of civilisation; but M. De Candolle has shown that this probably has seldom occurred. As soon as a plant was 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 become extinct; 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 (9/4. "Considerations sur les Cereales" 1842 page 37. "Geographie Bot." 1855 page 930. "Plus on suppose l"agriculture ancienne et remontant a une epoque d"ignorance, plus il est probable que les cultivateurs avaient choisi des especes offrant a l"origine meme un avantage incontestable.") 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 (9/5. Dr. Hooker has given me this information. See also his "Himalayan Journals" 1854 volume 2 page 49.), 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 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 (9/6. "Travels in Central Africa" English translation volume 1 pages 529 and 390; volume 2 pages 29, 265, 270. Livingstone "Travels" page 551.) states that the slaves over a large part of the central region regularly collect the seeds of a wild gra.s.s, 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 of a wild gra.s.s, and farther south, as Andersson informs me, the natives largely use the seed of a gra.s.s 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 gra.s.ses in other parts of the world could be given. (9/7. For instance in both North and South America. Mr. Edgeworth "Journal Proc. Linn. Soc." vol 6 Bot. 1862 page 181 states that in the deserts of the Punjab poor women sweep up, "by a whisk into straw baskets," the seeds of four genera of gra.s.ses, namely, of Agrostis, Panic.u.m, Cenchrus, and Pennisetum, as well as the seeds of four other genera belonging to distinct families.)
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, etc., 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, beechmast, and other wild berries and fruit. (9/8. Prof. O. Heer "Die Pflanzen der Pfahlbauten" 1866 aus dem Neujahr. Naturforsch. Geselschaft" 1866; and Dr.
H. Christ in Rutimeyer"s "Die Fauna der Pfahlbauten" 1861 s. 226.) Jemmy b.u.t.ton, 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 (9/9. "Travels" page 535. Du Chaillu "Adventures in Equatorial Africa" 1861 page 445.) 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 the seeds of useful plants; and as the soil near the hovels of the natives (9/10. In Tierra del Fuego the spot where wigwams had formerly stood could be distinguished at a great distance by the bright green tint of the native vegetation.) 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. (9/11. "American Acad. of Arts and Sciences" April 10th, 1860 page 413. Downing "The Fruits of America" 1845 page 261.) 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 (9/12. "Journals of Expeditions in Australia" 1841 volume 2 page 292.) never saw this law, evidently framed for the preservation of the plant, violated. We see the same spirit in the superst.i.tious belief of the Fuegians, that killing water-fowl whilst very young will be followed by "much rain, snow, blow much." (9/13. Darwin "Journal of Researches" 1845 page 215.) 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 ma.s.s.
It has often been remarked (9/14. De Candolle has tabulated the facts in the most interesting manner in his "Geographie Bot." page 986.) 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 canary-gra.s.s, 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 be indeed 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 (9/15. "Flora of Australia" Introduction page 110.) 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 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 civilised 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 and cultivated. In North America (9/16. For Canada see J. Cartier"s Voyage in 1534; for Florida see Narvaez and Ferdinand de Soto"s Voyages. As I have consulted these and other old Voyages in more than one general collection of Voyages, I do not give precise references to the pages. See also for several references Asa Gray in the "American Journal of Science" volume 24 November 1857 page 441. For the traditions of the natives of New Zealand see Crawfurd "Grammar and Dict. of the Malay Language" 1852 page 260.) the natives cultivated maize, pumpkins, gourds, beans, and peas, "all different from ours," and tobacco; and we are hardly justified in a.s.suming that none of our present plants are descended from these North American forms. Had North America been civilised 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 mult.i.tude 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." (9/17. See for example Mr. Hewett C. Watson"s remarks on our wild plums and cherries and crabs: "Cybele Britannica"
volume 1 pages 330, 334, etc. Van Mons (in his "Arbres Fruitiers" 1835 tome 1 page 444) declares that he has found the types of all our cultivated varieties in wild seedlings, but then he looks on these seedlings as so many aboriginal stocks.)
[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 (9/18. See A. De Candolle "Geograph. Bot." 1855 page 928 et seq. G.o.dron "De l"Espece" 1859 tome 2 page 70; and Metzger "Die Getreidearten" etc. 1841.) 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 mult.i.tude 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 (9/19. Mr. Bentham in his review ent.i.tled "Hist. Notes on cultivated Plants" by Dr. A. Targioni- Tozzetti in "Journal of Hort. Soc." volume 9 1855 page 133. He informs me that he still retains the same opinion.), "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 (9/20. "Geograph. Bot." page 928. The whole subject is discussed with admirable fulness and knowledge.) has adduced abundant evidence that common wheat (Tritic.u.m vulgare) has been found wild in various parts of Asia, where it is not likely to have escaped from cultivation: and there is some force in M. G.o.dron"s remark, that, supposing these plants to be escaped seedlings (9/21. G.o.dron "De l"Espece" tome 2 page 72. A few years ago the excellent, though misinterpreted, observations of M. Fabre led many persons to believe that wheat was a modified descendant of Aegilops; but M.
G.o.dron (tome 1 page 165) has shown by careful experiments that the first step in the series, viz. Aegilops triticoides, is a hybrid between wheat and Ae. ovata. The frequency with which these hybrids spontaneously arise, and the gradual manner in which the Ae. triticoides becomes converted into true wheat, alone leave any doubt with respect to M. G.o.dron"s conclusions.), as 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.
But the strong tendency to inheritance, which most of the varieties of wheat evince, as we shall presently see, is here greatly undervalued. Much weight must also be attributed to a remark by Professor Hildebrand (9/22.
"Die Verbreitungsmittel der Pflanzen" 1873 page 129.) that when the seeds or fruit of cultivated plants possess qualities disadvantageous to them as a means of distribution, we may feel almost sure that they no longer retain their aboriginal condition. On the other hand, 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. Buckmann (9/23. Report to British a.s.sociation for 1857 page 207.), 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, G.o.dron 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 (9/24. Considerations sur les Cereales" 1842-43 page 29.) speaks of three new species or varieties, sent to Europe in 1822 from Chinese Mongolia, which he considers as being there indigenous. Moorcroft (9/25. "Travels in the Himalayan Provinces"
etc. 1841 volume 1 page 224.) 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 have arisen so strongly marked, 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 (9/26. Col. J. Le Couteur on the "Varieties of Wheat" pages 23, 79.); 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 (9/27. Loiseleur-Deslongchamps "Consid.
sur les Cereales" page 11.) differ in colour and in shape, being quadrangular, compressed, or nearly cylindrical; and the florets differ in their approximation to each other, in their p.u.b.escence, 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 (9/28. See an excellent review in Hooker "Journ. of Botany" volume 8 page 82 note.); although, as remarked by G.o.dron (9/29. "De l"Espece" tome 2 page 73.) the presence of barbs is variable in certain wild gra.s.ses, 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 h.o.r.n.y, and in the proportion of gluten which they contain.
Nearly all the races or species of wheat vary, as G.o.dron (9/30. Ibid tome 2 page 75.) 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, etc. 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 const.i.tution, 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.
(9/31. For Dalbret and Philippar see Loiseleur-Deslongchamps "Consid. sur les Cereales" pages 45, 70. Le Couteur on Wheat pages 6, 14-17.) 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, he found that there was only one "secure mode to ensure the growth of pure sorts, namely, to grow them from single grains or from single ears, and to follow up the plan by afterwards sowing only the produce of the most productive so as to form a stock." But Major Hallett (9/32. See his Essay on "Pedigree in Wheat" 1862; also paper read before the British a.s.sociation 1869 and other publications.) has gone much farther, and by the continued selection of plants from the grains of the same ear, during successive generations, has made his "Pedigree in Wheat"
(and other cereals) now famous in many quarters of the world. 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 (9/33.
"Varieties of Wheat" Introduction page 6. Marshall in his "Rural Economy of Yorkshire" volume 2 page 9 remarks that "in every field of corn there is as much variety as in a herd of cattle.") 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 sometimes suddenly appear: thus Mr. Shirreff has had the good fortune to raise in his lifetime seven new varieties, which are now extensively grown in many parts of Britain. (9/34. "Gardener"s Chronicle" and "Agricult.
Gazette" 1862 page 963.)
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. On the other hand Major Hallett (9/35. "Gardener"s Chronicle" November 1868 page 1199.) has shown how wonderfully constant some varieties are, although not ancient ones, and although cultivated in various countries. With respect to the tendency to vary, Metzger (9/36. "Getreidearten" 1841 s. 66, 91, 92, 116, 117.) 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 a.s.sumed 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.