in discussing the quality of wheat it is necessary to adopt two distinct points of view, that of the farmer and that of the miller. a good wheat from 28 the farmer’s point, of view is one that will year by year give him a good monetary return per acre. now the monetary return obviously depends on two factors, the yield per acre and the value per quarter, coomb, or bushel, as the case may be. these two factors are quite independent and must be discussed separately.
we will first confine our attention to the yield per acre. this has already been shown to depend on the presence in the soil of plenty of the various elements required by plants, in the case of wheat nitrogen being especially important. the need of suitable soil and proper cultivation has also been emphasised. these conditions are to a great extent under the control of the farmer, whose fault it is if they are not efficiently arranged. but there are other factors affecting the yield of wheat which cannot be controlled, such for instance as sunshine and rainfall. the variations in these conditions from year to year are little understood, but they are now the subject of accurate study, and already dr w. n. shaw, the chief of the meteorological office has suggested a periodicity in the yield of wheat, connected with certain climatic conditions, notably the autumnal rainfall.
we have left to the last one of the most important factors which determine the yield of wheat, namely, the choice of the particular variety which is sown. this is undoubtedly one of the most important points 29 in wheat-growing which the farmer has to decide for himself. the british farmer has no equal as a producer of high class stock. he supplies pedigree animals of all kinds to the farmers of all other lands, and he has attained this preeminence by careful attention to the great, indeed the surpassing, importance of purity of breed. it is only in recent years that the idea has dawned on the agricultural community that breed is just as important in plants as in animals. it is extraordinary that such an obvious fact should have been ignored for so long. that it now occupies so prominently the attention of the farmers is due to the work of the agricultural colleges and experiment stations in sweden, america, and many other countries, and last but by no means least in great britain. this demonstration of the value of plant breeding is perhaps the greatest achievement in the domain of agricultural science since the publication of lawes and gilbert’s classical papers on the manurial requirements of crops.
wheat is not only one of the most adaptable of plants. it is also one of the most plastic and prone to variation. during the many centuries over which its cultivation has extended it has yielded hundreds of different varieties, whose origin, however, except in a few doubtful cases is unknown. comparatively few of these varieties are in common use in this country, and even of these it was impossible until recently to 30 31 say which was the best. it was even almost impossible to obtain a pure stock of many of the standard varieties. this is by no means the simple matter it appears to be. it is of course quite easy to pick out a single ear, to rub out the grain from it, to sow the grain on a small plot by itself and to raise a pound or so of perfectly pure seed. this can again be sown by itself, and the produce, thrashed by hand, will give perhaps a bushel of seed which will be quite pure. from this seed it will be possible to sow something like an acre; and now the trouble begins. any kind of hand thrashing is extremely tedious for the produce of acre plots, and thrashing by machinery becomes imperative. now a thrashing machine is an extremely complicated piece of apparatus, which it is practically impossible thoroughly to clean. when once seed has been through such a machine it is impossible to guarantee its purity. contamination in the thrashing machine is usually the cause of the impurity of the stocks of wheat and other cereals throughout the country. the only remedy is for the farmer to renew his stock from time to time from one or other of the seedsmen or institutions who make it their business to keep on hand pure stocks obtained by the method above described.
fig. 1. typical ears of a few of the many cultivated varieties of wheat
comparative trials of pure stocks of many of the standard varieties of wheat, and of the other cereals, are being carried out in almost every county by members 32 of the staff of the agricultural colleges. the object of such trials is to determine the relative cropping power of the different varieties. this might at first sight appear to be an extremely simple matter, but a moment’s consideration shows that this is not the case. no soil is so uniform that an experimenter can guarantee that each of the varieties he is trying has the same chance of making a good yield as far as soil is concerned. it is a matter of common knowledge too that every crop of wheat is more or less affected by insect and fungoid pests, whose injuries are unlikely to fall equally on each of the varieties in any variety test. many other causes of variation, such as unequal distribution of manure, inequalities in previous cropping of the land, irregular damage by birds, may well interfere with the reliability of such field tests.
much attention has been given to this subject during the last few years, and it has been shown that as often as not two plots of the same variety of wheat grown in the same field under conditions which are made as uniform as possible will differ in yield by 5 per cent. or more. obviously it is impossible to make comparisons of the cropping power of different varieties of wheat as the result of trials in which single plots of each variety are grown. it is a deplorable fact however that the results of most of the trials which are published are based on single plots only of the varieties compared. such results 33 can have no claim to reliability. single plots tests are excellent as local demonstrations, to give the farmers a chance of seeing the general characters of the various wheats in the field, but for the determination of cropping power their results are misleading. for the comparison of two varieties however an accuracy of about 1 per cent., which is good enough for the purpose in view, can be obtained by growing, harvesting and weighing separately, five separate plots of each variety under experiment, provided the plots are distributed in pairs over the experimental field.
still greater accuracy can be attained by growing very large numbers of very small plots of each variety in a bird-proof enclosure. the illustration shows such an enclosure at cambridge where five varieties were tested, each on 40 plots. each plot was one square yard, and the whole 200 plots occupied so small an area that uniformity of soil could be secured by hand culture.
several experimenters are now at work on these lines, and it is to be hoped that all who wish to carry out variety tests will either follow suit, or content themselves with using their single plots only for demonstrating the general characters of the varieties in the field.
so far we have confined our discussion to the standard varieties, and we must now turn our 34 35 attention to the work which has been done in recent years on the breeding of new varieties which will yield heavier crops than any of the varieties hitherto in cultivation.
fig. 2. part of bird-proof enclosure containing many small plots for variety testing
it is impossible to give more than a very brief outline of the vast amount of work which has been done on this subject. broadly speaking, two methods have been used, selection and hybridisation. of these selection is the simpler, but even selection is by no means the simple matter it might appear to be. let us examine for a moment the various characters of a single wheat plant which determine its capacity for yielding grain. the average weight of one grain, the number of grains in an ear, the number of ears on the plant, are obviously all of them characters which will influence the weight of grain yielded by the plant. many experimenters have examined thousands of plants for these characters, often by means of extremely ingenious mechanical sorting instruments, and have raised strains of seed from the plants showing one or more of these characters in the highest degree. the results of this method of selection have as a rule been unsuccessful, no doubt because the size of the grain, the number of grains in the ear, and the number of ears on the plant, are so largely determined by the food supply, or by some other cause quite outside the plant itself. they are in fact in most cases acquired characters, and are not inherited. 36 this method of selection results in picking out rather the well nourished plant than the well bred one. again it is obvious that the weight of grain per acre is measured by the weight of one grain, multiplied by the number of grains per ear, multiplied by the number of ears per plant, multiplied by the number of plants per acre. selecting for any one of these characters, say large ears, is quite likely to diminish other equally important characters, say number of ears per plant.
in order to avoid these difficulties the method of selection according to progeny has been devised. the essence of this method is to select for stock, not the best individual plant, but the plant whose progeny yields the greatest weight of seed per unit area. this method was applied with great industry and some success in the minnesota wheat breeding experiments of willett hays. large numbers of promising plants were collected from a plot of the best variety in that district. the seed from each plant was rubbed out and sown separately. one hundred seeds from each plant were sown on small separate plots which were carefully marked out and labelled. every possible precaution was taken to make all the little plots uniform in every way. by harvesting each plot separately, and weighing the grain it produced, it was possible to find out which of the original plants had given the largest yield. this process 37 was repeated by sowing again on separate plots a hundred seeds from each individual plant from the best plot, and again weighing the produce of each plot. after several repetitions it was stated that new strains were obtained which yielded considerably greater crops than the variety from which they were originally selected. these results were published in 1895, but no definite statements have since appeared as to the success ultimately attained.
this method of selection is undoubtedly more likely to give successful results than the method which depends on the selection of plants for their apparent good qualities; but it has several weak points. in the first place it is almost impossible to make the soil of a large number of plots so uniform that variation in yield due to varying soil conditions will not mask the variations due to the different cropping power of the seed of the separate plants. many experimenters are still at work with a view to overcome this difficulty. secondly, plant breeders are by no means agreed on the exact theoretical meaning of improvement by selection. the balance of evidence at the present time seems to tend towards the general adoption of what is known as the pure-line theory. according to this theory, which was first enunciated by johannsen of copenhagen as the outcome of a lengthy series of experiments with beans, the general population of plants, in say a field 38 of wheat of one of the standard varieties giving an average yield of say 40 bushels per acre, consists of a very large number of races each varying in yielding capacity from say 30 to 50 bushels per acre. these races can be separated by collecting a very large number of separate plants, sowing say 100 seeds from each on a separate plot, and weighing the produce separately. the crop on each plot, being the produce of a separate plant, will be a distinct race, or pure line as it is called, and each pure line will possess a definite yielding power of its own. if this is so the difficulty of soil variation can be overcome by saving seed from many of the best plots, and sowing it on several separate plots. at harvest time these are gathered separately and weighed. by averaging the weights of grain from many separate plots scattered over the experimental area the effect of soil variation can be eliminated.
the method is very laborious, but seems to promise successful results. for instance, beaven of warminster, working on these lines, has succeeded in isolating a pure line of archer barley which is a distinct advance on the ordinary stocks of that variety. there appears to be no reason why it should not be applied to wheat with equal success; in fact, percival of reading states that his selected blue cone wheat was produced in this way. the essence, of the method is that if the pure-line theory 39 holds there is no necessity to continue selecting the best individual plant from each plot, for each plot being the produce of a single plant must be a pure line with its own definite characters. the whole of the seed from a number of the best plots can therefore be saved. the seed from each of these good plots can be used to sow many separate plots: by averaging the yields from these plots the effects of soil variation can be eliminated, and the cropping power thus determined with great accuracy. it is thus possible to pick out the best pure line with far greater certainty than in any other way. it must not be forgotten, however, that the success of the method depends on the truth of the pure-line theory. it should also be pointed out that the cereals are all self-fertilised plants. when working on these lines with plants which are readily cross-fertilised, such for instance as turnips or mangels, it is necessary to enclose the original individual plants, and the subsequent separate plots, so as to prevent them from crossing with plants of other lines, in which case the progeny would be cross-bred and not the progeny of a single plant. this of course enormously increases the difficulty of carrying out the experiment. enough has been said to show that the task of improving plants by systematic selection is an extremely tedious and difficult one. of course anyone may be fortunate enough to drop on a valuable sport when carefully 40 inspecting his crops, and it appears likely that many of the most valuable varieties in cultivation have originated from lucky chances of this kind.
it has always been the dream of the plant breeder to make use of the process of hybridisation for creating new varieties, but until the work of mendel threw new light on the subject the odds were against the success of the breeder. the idea of the older hybridisers was that crossing two dissimilar varieties broke the type and gave rise to greatly increased variation. from the very diverse progeny resulting from the cross, likely individuals were picked out. seed was saved from these and sown on separate plots, and attempts were made to obtain a fixed type by destroying, or roguing as it is called, all the plants which departed from the desired type. this was a tedious process which seldom resulted in success. mendel’s discoveries, made originally nearly 50 years ago, as the result of experiments in the garden of his monastery, in the crossing of different varieties of garden peas, remained unknown until rediscovered in 1899. in the 12 years which have elapsed since that date the results which have been achieved show clearly that the application of mendelian methods is likely greatly to increase the simplicity and the certainty of plant improvement by hybridisation.
fig. 3. a wheat flower with the chaff opened to show the stamens and the stigmas
perhaps the best way of describing the bearing of mendel’s laws on the improvement of wheat is to 41 give an illustration from the work carried out by biffen at cambridge, dealing at first with simple characters obvious to anyone. in one of his first experiments two varieties of wheat were crossed with each other. the one variety possessed long loose beardless ears, the other short dense bearded ears. 42 the crossing was performed early in june, sometime before what the farmer calls flowering time. the flowering of wheat as understood by the farmer is the escape of the stamens from the flower. fertilisation always takes place before this, and crossing must be done of course before self-fertilisation has been effected. the actual crossing is done thus: an ear of one of the varieties having been chosen, one of the flowers is exposed by opening the chaff which encloses it (fig. 3), the stamens are removed by forceps, and a stamen from a flower of the other variety is inserted, care being taken that it bursts so that the pollen may touch the feathery stigmas. the chaff is then pushed back so that it may protect the flower from injury. the pollen grains grow on the stigmas, and penetrate down the styles into the ovary. in this way cross-fertilisation is effected. it is usual to operate on several flowers on an ear in this way, and to remove the other flowers, so that no mistake may be made as to which seed is the result of the cross. immediately after the operation the ear is usually tied up in a waxed paper bag. this serves to make it absolutely certain that no other pollen can get access to the stigmas except that which was placed there. at the same time it is a convenient way of marking the ear which was experimented upon. the cross is usually made both ways, each variety being used both as pollen parent and as ovary 43 parent. as soon as the cross-fertilised seeds are ripe they are gathered, and early in the autumn they are sown. it is almost necessary to sow them and other small quantities of seed wheat in an enclosure 44 protected by wire netting. otherwise they are very liable to suffer great damage from sparrows. the plants which grow from the cross-fertilised seeds are known as the first generation. in the case under consideration, they were found to produce ears of medium length and denseness, intermediate between the ears of the two parent varieties, and to be beardless. the first generation plants were also characterised by extraordinary vigour, as is the case with almost all first crosses, both in plants and animals. their seed was saved and sown on a small plot, and produced some hundreds of plants of the second generation. on examining these second generation plants it was found that the characters of the parent varieties had rearranged themselves in every possible combination, long ears with and without beard, short ears with and without beard, intermediate ears with and without beard, as shown in fig. 4. these different types were sorted out and counted, when they were found to be present in perfectly definite proportions. this is best shown in the form of a tabulated statement, thus:
ears
long
beardless ears
long
bearded ears
medium
beardless ears
medium
bearded ears
short
beardless ears
short
bearded
3 1 6 2 3 1
translating this into words, out of every 16 plants in the second generation there were four long eared 45 plants, three beardless and one bearded; eight plants with ears of intermediate length, six beardless and two bearded; and four short eared plants, three beardless and one bearded. the illustration shows all these types. the experiment has been repeated several times and the same proportions were invariably obtained. the result, too, was independent of the way the cross was made. seed was collected separately from large numbers of single plants of each type. the seed from each plant was sown by itself in a row, so that its progeny could be separately observed. it was found that all the plants of the second generation possessing ears of intermediate length produced in the third generation plants with long ears, short ears, and medium ears in the proportion of 1 : 1 : 2, the same proportion in fact as in the second generation. short eared plants produced only short eared offspring, long eared plants only long eared offspring. bearded plants produced only bearded offspring. beardless plants, however, produced in some cases only beardless offspring, in other cases both beardless and bearded offspring in the proportion of three of the former to one of the latter. out of every three beardless plants only one was found to breed true, whilst two gave a mixed progeny. it appears therefore that in the second generation some of the types which occur breed true, whilst others do not. some of the true breeding 46 individuals can be picked out at sight, for instance, those with long or short bearded ears. some of those which will not breed true can also be recognised by inspection, for instance, all the plants with ears of intermediate length. in other cases it is only possible to pick out the individual plants which breed true by growing their seed and observing how it behaves. if it produces progeny all of which are like the plant from which the seed was obtained, that plant is a fixed type and will breed true continuously in the future. the final result of the experiment was to obtain in three years from the time the cross was made, four fixed types which subsequent experience has shown breed true continuously, a long eared bearded type, a short eared beardless type, a long eared beardless type and a short eared bearded type. of these the second two are exactly like the two parental varieties, but the first two are new, each combining one character from each parent. these fixed types already existed in the second generation. mendel’s discoveries with peas showed how to pick them out. obviously there is no need for the years of roguing by which the older hybridisers used to attempt to fix their desired type. all the types are present in the second generation. mendel has shown how the fixed ones may be picked out.
fig. 4. p, p, the two parental types. f? the first cross. f?, 1-6, the types found in the second generation
the characters described above are not of any great economic importance. biffen has shown that 47 such important characters as baking strength and resistance to the disease known as yellow rust behave on crossing in the same way as beard. working on the lines of the experiment described above he has succeeded in producing several new varieties which in baking strength and in rust resistance are a distinct advance on any varieties in cultivation in this country. his method of working was to collect wheats from every part of the world, to sow them and to pick out from the crop, which was usually a mixed one, all the pure types he could. these were grown on small plots for several years under close observation. many were found to be worthless and were soon discarded. others were observed to possess some one valuable character. amongst these a pure strain of red fife was obtained from canadian seed, which was found to retain when grown in england the excellent baking strength of the hard wheats of canada and north america. again, other varieties were noticed to remain free from yellow rust year after year, even when varieties on adjoining plots were so badly infected that they failed to produce seed. other varieties, too, were preserved for the sturdiness of their straw, their earliness in ripening, vigour of growth, or yielding capacity. many crosses were made with these as parents. the illustration shows a corner of the cambridge wheat-breeding enclosure including a 48 49 miscellaneous collection of parent varieties. the paper bags on the ears show where crosses have been made. from the second generation numbers of individual plants possessing desirable characters were picked out, and the fixed types isolated in the third generation by making cultures from the seed of these single plants. the seed from these fixed types was sown on small field plots, at which stage many had to be rejected because they were found wanting in some character of great practical importance which did not make itself evident in the breeding enclosure. the illustration shows a case in point. it was photographed after heavy rain in july. the weakness of the straw of the variety on the left had not been noticed in the enclosure. the types which approved themselves on the small field plots were again grown on larger plots so that their yield and milling and baking characters could be tested. so far two types have survived the ordeal. one combines the cropping power of the best english varieties with the baking strength of north american hard wheat. it is the outcome of a cross between rough chaff and red fife. its average crop in 1911 was 38 bushels per acre as the result of 28 independent trials, and, where the local millers have found out its quality, it makes on the market four or five shillings per quarter more than the ordinary english varieties. the other resulted from a cross between square 50 51 head’s master and a rust-resisting type isolated from a graded russian wheat called ghirka. it is practically rust-proof. consequently it yields a heavier crop than any of the ordinary varieties which are all more or less susceptible to rust. the presence of rust in and on the leaves hinders the growth of the plant, lowers the yield, and increases the proportion of shrivelled grains. it has been estimated that rust diminishes the world’s wheat crop by something like one third. the new rust-proof variety gave an average yield of about 6 bushels per acre more than ordinary varieties on the average of 28 trials last year. it is called little joss and is especially valuable in the fens and other districts where rust is more than usually virulent.
