Chapter D: Eversporting Varieties (20)

Apart from these considerations the improvement reached in half a century or in about twenty to thirty generations is not suggestive of anything absolute. Everything is fluctuating now, even as it was at the outset, and equally dependent on continual care. Vilmorin has given some figures for the beets of the first generations from which he started his race. He quotes 14% as a recommendable amount, and 7 and 21 as the extreme instances of his analyses. However incorrect these figures may be, they coincide to a striking degree with the present condition of the best European races. Of course minor values are excluded each year by the selection, and in consequence the average value has increased. For the year 1874 we find a standard of 10-14% considered as normal, [797] bad years giving 10%, good years from 12% to 14% in the average. Extreme instances exceeded 17%. From that time the practice of the polarization of the juice for the estimate of the sugar has rapidly spread throughout Europe, and a definite increase of the average value soon resulted. This however, often does not exceed 14%, and beets selected in the field for the purpose of polarization come up to an average of 15 to 16%, varying downward to less than 10% and upward to 20 and 21%. In the main the figures are the same as those of Vilmorin, the range of variability has not been reduced, and higher extremes are not reached. An average increase of 1% is of great practical importance, and nothing can excel the industry and care displayed in the improvement of the beet-races. Notwithstanding this a lasting influence has not been exercised; the methods of selection have been improved, and the number of polarized beets has been brought up to some hundreds of thousands in single factories, but the improvement is still as dependent upon continuous selection as it was half a century ago.

The process is practically very successful, but the support afforded by it to the selection theory vanishes on critical examination.

[798]

LECTURE XXVIII

ARTIFICIAL AND NATURAL SELECTION

The comparison of artificial and natural selection has furnished material support for the theory of descent, and in turn been the object of constant criticism since the time of Darwin. The criticisms, in greater part, have arisen chiefly from an imperfect knowledge of both processes. By the aid of distinctions recently made possible, the contrast between elementary species and improved races has become much more vivid, and promises to yield better results on which to base comparisons of artificial and natural selection.

Elementary species, as we have seen in earlier lectures, occur in wild and in cultivated plants. In older genera and systematic species they are often present in small numbers only, but many of the more recent wild types and also many of the cultivated forms are very rich in this respect. In agriculture the choice of the most adequate elementary forms for any special purpose is acknowledged [799] as the first step in the way of selection, and is designated by the name of variety-testing, applying the term variety to all the subdivisions of systematic species indiscriminately. In natural processes it bears the title of survival of species. The fact that recent types show large numbers, and in some instances even hundreds of minor constant forms, while the older genera are considerably reduced in this respect, is commonly explained by the assumption of extinction of species on a correspondingly large scale. This extinction is considered to affect the unfit in a higher measure than the fit. Consequently the former vanish, often without leaving any trace of their existence, and only those that prove to be sufficiently adapted to the surrounding external conditions, resist and survive.

This selection exhibits far-reaching analogies between the artificial and the natural processes, and is in both cases of the very highest importance. In nature the dying out of unfit mutations is the result of the great struggle for life. In a previous lecture we have compared its agency with that of a sieve. All elements which are too small or too weak fall through, and only those are preserved which resist the sifting process. Reduced in number they thrive and multiply and are thus enabled to [800] strike out new mutative changes. These are again submitted to the sifting tests, and the frequent repetition of this process is considered to give a good explanation of the manifold, highly complicated, and admirable structures which strike the beginner as the only real adaptations in nature.

Exactly in the same way artificial selection isolates and preserves some elementary species, while it destroys others. Of course the time is not sufficient to secure new mutations, or at least these are only rare at present, and their occurrence is doubtful in historic periods. Apart from this unavoidable difference the analogy between natural and artificial selection appears to me to be very striking.

This form of selection may be termed selection between species. Opposed to it stands the selection within the elementary species or variety. It has of late, alone come to be known as selection, though in reality it does not deserve this distinction. I have already detailed the historical evidence which gives preference to selection between species. The process can best be designated by the name of intraspecific selection, if it is understood that the term intraspecific is meant to apply to the conception of small or elementary species.

I do not wish to propose new terms, but [801] I think that the principal differences might better become understood by the introduction of the word election into the discussion of questions of heredity. Election meant formerly the preferential choice of single individuals, while the derivation of the word selection points to a segregation of assemblies into their larger parts. Or to state it in a shorter way, individual selection is exactly what is usually termed election. Choosing one man from among thousands is to elect him, but a select party is a group of chosen persons. There would be no great difficulty in the introduction of the word election, as breeders are already in the habit of calling their choice individuals "elite," at least in the case of beets and of cereals.

This intraspecific selection affords a second point for the comparison between natural and artificial processes. This case is readily granted to be more difficult than the first, but there can be no doubt that the similarity is due to strictly comparable causes. In practice this process is scarcely second in importance to the selection between species, and in numerous cases it rests upon it, and crowns it, bringing the isolated forms up to their highest possible degree of usefulness. In nature it does quite the same, adapting strains of individuals to the local conditions of their environment. Improved [802] races do not generally last very long in practice; sooner or later they are surpassed by new selections. Exactly so we may imagine the agency of natural intraspecific selection. It produces the local races, the marks of which disappear as soon as the special external conditions cease to act. It is responsible only for the smallest lateral branches of the pedigree, but has nothing in common with the evolution on the main stems. It is of very subordinate importance.

These assertions of course, are directly opposed to the current run of scientific belief, but they are supported by facts. A considerable part of the evidence has already been dealt with and for our closing discussion only an exact comparison remains to be made between the two detailed types of intraspecific selection. In coming to this I will first dwell upon some intermediate types and conclude with a critical discussion of the features of artificial selection, which to my mind prove the invalidity of the conclusions drawn from it in behalf of an explanation of the processes of nature.

Natural selection occurs not only in the wild state, but is also active in cultivated fields. Here it regulates the struggle of the selected varieties and improved races with the older types, and even with the wild species. In a previous [803] lecture I have detailed the rapid increase of the wild oats in certain years, and described the experiments of Risler and Rimpau in the running out of select varieties. The agency is always the same. The preferred forms, which give a larger harvest, are generally more sensitive to injurious influences, more dependent on rich manure and on adequate treatment. The native varieties have therefore the advantage, when climatic or cultural conditions are unfavorable for the fields at large. They suffer in a minor degree, and are thereby enabled to propagate themselves afterwards more rapidly and to defeat the finer types. This struggle for life is a constant one, and can easily be followed, whenever the composition of a strain is noted in successive years. It is well appreciated by breeders and farmers, because it is always liable to counteract their endeavors and to claim their utmost efforts to keep their races pure. There can be no doubt that exactly the same struggle exempt from man's intrusion is fought out in the wild state.

Local races of wild plants have not been the object for field observations recently. Some facts however, are known concerning them. On the East Friesian Islands in the North Sea the flowers are strikingly larger and brighter colored than those of the same species on the [804] neighboring continent. This local difference is ascribed by Behrens to a more severe selection by the pollinating insects in consequence of their lesser frequency on these very windy isles. Seeds of the pines from the Himalayas yield cold-resisting young plants if gathered from trees in a high altitude, while the seeds of the same species from lower regions yield more sensitive seedlings. Similar instances are afforded by _Rhododendron_ and other mountain species. According to Cieslar corresponding differences are shown by seeds of firs and larches from alpine and lowland provinces.

Such changes are directly dependent on external influences. This is especially manifest in experiments extending the cultures in higher or in more northern regions. The shorter summer is a natural agent of selection; it excludes all individuals which cannot ripen their seeds during so short a period. Only the short lived ones survive. Schubeler made very striking experiments with corn and other different cereals, and has succeeded in making their culture possible in regions of Norway where it formerly failed. In the district of Christiania, corn had within some few years reduced its lifetime from 123 to 90 days, yielding smaller stems and fewer kernels, but still sufficient to make its culture profitable under the existing conditions. [805] This change was not permanent, but was observed to diminish rapidly and to disappear entirely, whenever the Norwegian strain was cultivated in the southern part of Germany. It was a typical improved race, dependent on continual selection by the short summers which had produced it. Similar results have been reached by Von Wettstein in the comparison of kinds of flax from different countries. The analogy between such cultivated local races and the local races of nature is quite striking. The practice of seed exchange rests for a large part on the experience that the characters, acquired under the definite climatic and cultural conditions of some select regions, hold good for one or two, and sometimes even more generations, before they decrease to practical uselessness. The Probstei, the Hanna and other districts owe their wealth to this temporary superiority of their wheat and other cereals.

Leaving these intermediate forms of selection, we now come to our principal point. It has already been discussed at some length in the previous lecture, but needs further consideration. It is the question whether intraspecific selection may be regarded as a cause of lasting and ever-increasing improvement. This is assumed by biologists who consider fluctuating variability as the main source of progression [806] in the organic world. But the experience of the breeders does not support this view, since the results of practice prove that selection according to a constant standard soon reaches a limit which it is not capable of transgressing. In order to attain further improvements the method of selection itself must be improved. A better and sharper method assures the choice of more valuable representatives of the race, even if these must be sought for in far larger numbers of individuals, as is indicated by the law of Quetelet.

Continuous or even prolonged improvement of a cultivated race is not the result of frequently repeated selection, but of the improvement of the standard of appreciation. Nature, as far as we know, changes her standard from time to time only in consequence of the migrations of the species, or of local changes of climate. Afterwards the new standard remains unchanged for centuries.

Selection, according to a constant standard, reaches its results in few generations. The experience of Van Mons and other breeders of apples shows that the limit of size and lusciousness may be soon attained. Vilmorin's experiments with wild carrots and those of Carriere with radishes lead to the same conclusion as regards roots. Improvements of flowers in [807] size and color are usually easy and rapid in the beginning, but an impassable limit is soon reached. Numerous other instances could be given.

Contrasted with these simple cases is the method of selecting sugar beets. More than once I have alluded to this splendid example of the influence of man upon domestic races, and tried to point out how little support it affords to the current scientific opinion concerning the power of natural selection. For this reason it is interesting to see how a gradual development of the methods of selection has been, from the very outset, one of the chief aims of the breeders. None of them doubts that an improvement of the method alone is adequate to obtain results. This result, in the main, is the securing of a few percent more of sugar, a change hardly comparable with that progress in evolution, which our theories are destined to explain.

Vilmorin's original method was a very simple one. Polarization was still undiscovered in his time. He determined the specific weight of his beets, either by weighing them as a whole, or by using a piece cut from the base of the roots and deprived of its bark, in order to test only the sugar tissues. The pieces were floated in solutions of salt, which were diluted until the pieces [808] began to sink. Their specific weight at that moment was determined and considered to be a measure of the corresponding value of the beet. This principle was afterwards improved in two ways. The first was a selection after the salt solution method, but performed on a large scale. After some few determinations, a solution was made of such strength as to allow the greater number of the beets to float, and only the best to sink down. In large vessels thousands of beets could be tested in this way, to select a few of the very heaviest. The other improvement was the determination of the specific weight of the sap, pressed out from the tissue. It was more tedious and more expensive, but more direct, as the influence of the air cavities of the tissue was excluded. It prepared the way for polarization.

This was introduced about the year 1874 in Germany, and soon became generally accepted. It allowed the amount of sugar to be measured directly, and with but slight trouble. Thousands of beets could be tested yearly by this method, and the best selected for the production of seed. In some factories a standard percentage is determined by previous inquiries, and the mass of the beets is tested only by it. In others the methods of taking samples and clearing the sap have been improved so far as to allow the [809] exact determination of three hundred thousand polarization values of beets within a few weeks. Such figures give the richest material for statistical studies, and at once indicate the best roots, while they enable the breeder to change his standard in accordance with the results at any time. Furthermore they allow the mass of the beets to be divided into groups of different quality, and to produce, besides the seeds for the continuation of the race, a first class and second-class product and so on. In the factory of Messrs. Kuhn & Co., at Naarden, Holland, the grinding machine has been markedly improved, so as to tear all cell walls asunder, open all cells, and secure the whole of the sap within less than a minute, and without heating.

It would take too long to go into further details, or to describe the simultaneous changes that have been applied to the culture of the elite strains. The detailed features suffice to show that the chief care of the breeder in this case is a continuous amelioration of the method of selecting. It is manifest that the progression of the race is in the main due to great technical improvements, and not solely to the repetition of the selection.

Similar facts may be seen on all the great lines of industrial selection. An increasing appreciation [810] of all the qualities of the selected plants is the common feature. Morphological characters, and the capacity of yielding the desired products, are the first points that strike the breeder. The relation to climate and the dependence on manure soon follow; but the physiological and chemical sides of the problem are usually slow of recognition in the methods of selection. When visiting Mr. de Vilmorin at Paris some years ago, I inspected his laboratory for the selection of potatoes. In the method in use, the tubers were rubbed to pulp and the starch was extracted and measured. A starch percentage figure was determined for each plant, and the selection of the tubers for planting was founded upon this result. In the same way wheat has been selected by Dippe at Quedlinburg, first by a determination of its nitrogenous contents in general, and secondly by the amount of the substances which determine its value for baking purposes.

The celebrated rye of Schlanstedt was produced by the late Mr. Rimpau in a similar manner and was put on the market between 1880 and 1890 and was received with great favor throughout central Europe, especially in Germany and in France. It is a tall variety, with vigorous stems and very long heads, the kernels of which are nearly double the size of those of the [811] ordinary rye, and are seen protruding, when ripe, from between the scales of the spikelets. It is unfit for poor soils, but is one of the very best varieties for soils of medium fertility in a temperate climate. It is equal in the production of grain to the best French sorts, but far surpassing them in its amount of straw. It was perfected at the farm of Schlanstedt very slowly, according to the current conceptions of the period. The experiment was started in the year 1866, at which time Rimpau collected the most beautiful heads from among his fields, and sowed their kernels in his experiment garden. From this first culture the whole race was derived. Every year the best ears of the strain were chosen for repeated culture, under experimental care, while the remainder was multiplied in a field to furnish the seeds for large and continually increasing areas of his farms.

Two or three years were required to produce the quantity of seed of each kind required for all the fields of Schlanstedt. The experiment garden, which through the kindness of Mr. Rimpau I had the good fortune of visiting more than once between 1875 and 1878, was situated in the middle of his farm, at some distance from the dwellings. Of course it was treated with more care, and especially kept [812] in better conditions of fertility than was possible for the fields at large. A continued study of the qualities and exigencies of the elite plants accompanied this selection, and gave the means of gradually increasing the standard. Resistance against disease was observed and other qualities were ameliorated in the same manner. Mr. Rimpau repeatedly told me that he was most anxious not to overlook any single character, because he feared that if any of them might become selected in the wrong way, perchance unconsciously, the whole strain might suffer to such a degree as to make all the other ameliorations quite useless. With this purpose the number of plants per acre was kept nearly the same as those in the fields, and the size of the culture was large enough every year to include the best kernels of quite a number of heads. These were never separated, and exact individual pedigrees were not included in the plan. This mixture seemed to have the advantage of keeping up an average value of the larger number of the characters, which either from their nature or from their apparent unimportance had necessarily to be neglected.

After ten years of continuous labor, the rye of Rimpau caught the attention of his neighbors, being manifestly better than that of ordinary [813] sowings. Originally he had made his cultures for the improvement of his own fields only. Gradually however, he began to sell his product as seed to others, though he found the difference still very slight. After ten years more, about 1886, he was able to sell all his rye as seed, thereby making of course large profits. It is now acknowledged as one of the best sorts, though in his last letter Mr. Rimpau announced to me that the profits began to decline as other selected varieties of rye became known. The limit of productiveness was reached, and to surmount this, selection had to be begun again from some new and better starting point.

This new starting point invokes quite another principle of selection, a principle which threatens to make the contrast between artificial and natural selection still greater. In fact it is nothing new, being in use formerly in the selection of domestic animals, and having been applied by Vilmorin to his sugar beets more than half a century ago. Why it should ever have been overlooked and neglected in the selection of sugar beets now is not clear.

The principle in itself is very simple. It agrees that the visible characters of an animal or a plant are only an imperfect measure for its hereditary qualities, instead of being the real criterion to be relied upon, as is the current belief. [814] It further reasons that a direct appreciation of the capacity of inheritance can only be derived from the observation of the inheritance itself. Hence it concludes that the average value of the offspring is the only real standard by which to judge the representatives of a race and to found selection upon.

These statements are so directly opposed to views prevalent among plant breeders, that it seems necessary to deal with them from the theoretical and experimental, as well as from the practical side.

The theoretical arguments rest on the division of the fluctuating variability into the two large classes of individual or embryonic, and of partial deviations. We have dealt with this division at some length in the previous lecture. It will be apparent at once, if we choose a definite example. Let us ask what is the real significance of the percentage figure of a single plant in sugar beets. This value depends in the first place, on the strain or family from which the beet has been derived, but this primary point may be neglected here, because it is the same for all the beets of any lot, and determines the average, around which all are fluctuating.

The deviation of the percentage figure of a single beet depends on two main groups of external [815] causes. First come those that have influenced the young germs of the plant during its most sensitive period, when still an embryo within the ripening seed. They give a new limitation to the average condition, which once and forever becomes fixed for this special individual. In the second place the young seedling is affected during the development of its crown of leaves, and of its roots, by numerous factors, which cannot change this average, but may induce deviations from it, increasing or decreasing the amount of sugar, which will eventually be laid down in the root. The best young beet may be injured in many ways during periods of its lifetime, and produce less sugar than could reasonably be expected from it. It may be surpassed by beets of inferior constitution, but growing under more favorable circumstances.

Considered from this point of view the result of the polarization test is not a single value, but consists of at least two different factors. It may be equal to the algebraic sum of these, or to their difference, according to whether the external conditions on the field were locally and individually favorable or unfavorable. A large amount of sugar may be due to high individual value, with slight subsequent deviation from it, [816] or to a less prominent character combined with an extreme subordinate deviation.

Hence it is manifest that even the results of such a highly improved technical method do not deserve the confidence usually put in them. They are open to doubt, and the highest figures do not really indicate the best representatives of the race. In order to convey this conception to you in a still stronger manner, let us consider the partial variability as it usually shows itself. The various leaves of a plant may noticeably vary in size, the flowers in color, the fruits in flavor. They fluctuate around an average, which is assumed to represent the approximate value of the whole plant. But if we were allowed to measure only one leaf, or to estimate only one flower or fruit, and be compelled to conclude from it the worth of the whole plant, what mistakes we could make! We might indeed hit upon an average case, but we might as easily get an extreme, either in the way of increase or of decrease. In both cases our judgment would be badly founded. Now who can assure us that the single root of a given beet is an average representative of the partial variability? The fact that there is only one main root does not prove anything. An annual plant has only one stem, but a perennial species has many. The average height of the last is a [817] reliable character, but the casual height of the former is very uncertain.

So it is with the beets. A beet may be divided by its buds and give quite a number of roots, belonging to the same individual. These secondary roots have been tested for the amount of sugar, and found to exhibit a manifest degree of variability. If the first root corresponded to their average, it might be considered as reliable, but if not anyone will grant that an average is more reliable than a single determination. Deviations have as a fact been observed, proving the validity of our assertion. These considerations at once explain the disappointment so often experienced by breeders. Some facts may be quoted from the Belgian professor of agriculture at Gembloux, the late Mr. Laurent. He selected two beets, from a strain, with the exceptional amount of 23% sugar, but kept their offspring separate and analyzed some 60 of each. In both groups the average was only 11-12%, the extremes not surpassing 14-15%. Evidently the choice was a bad one, notwithstanding the high polarization value of the parent. Analogous cases are often observed, and my countrymen, Messrs. Kuhn & Co., go so far as to doubt all excessive variants, and to prefer beets with high, but less extraordinary percentages. Such are to be had in larger numbers [818] and their average has a good chance of exemption from a considerable portion of the doubts adhering to single excessive cases.

It is curious to note here what Louis de Vilmorin taught concerning this point in the year 1850. I quote his own words: "I have observed that in experiments on heredity it is necessary to individualize as much as possible. So I have taken to the habit of saving and sowing separately the seeds of every individual beet, and I have always found that among the chosen parent plants some had an offspring with a better average yield than others. At the end I have come to consider this character only, as a standard for amelioration."

The words are clear and their author is the originator of the whole method of plant breeding selection. Yet the principle has been abandoned, and nearly forgotten under the impression that polarization alone was the supreme guide to be relied upon. However, if I understand the signs rightly, the time is soon coming when Vilmorin's experience will become once more the foundation for progress in breeding.

Leaving the theoretical and historical aspects of the problem, we will now recall the experimental evidence, given in a former lecture, dealing with the inheritance of monstrosities. I have shown that in many instances monstrosities [819] constitute double races, consisting of monstrous and of normal individuals. At first sight one might be induced to surmise that the monstrous ones are the true representatives of the race, and that their seeds should be exclusively sown, in order to keep the strain up to its normal standard. One might even suppose that the normal individuals, or the so-called atavists, had really reverted to the original type of the species and that their progeny would remain true to this.

My experiments, however, have shown that quite the contrary is the case. No doubt, the seeds of the monstrous specimens are trustworthy, but the seeds of the atavists are not less so. Fasciated hawkweeds and twisted teasels gave the same average constitution of the offspring from highly monstrous, and from apparently wholly normal individuals. In other words the fullest development of the visible characteristic was not in the slightest degree an indication of better hereditary tendencies. In unfavorable years a whole generation of a fasciated race may exhibit exclusively normal plants, without transmitting a trace of this deficiency to the following generation. As soon as the suitable conditions return, the monstrosity reassumes its full development. The accordance of these facts with the experience [820] of breeders of domestic animals, and of Louis de Vilmorin, and with the result of the theoretical considerations concerning the factors of fluctuation has led me to suggest the method of selecting, which I have made use of in my experiments with tricotyls and syncotyls.

Seedling variations afford a means of counting many hundreds of individuals in a single germinating pan. If seed from one parent plant is sown only in each pan, a percentage figure for the amount of deviating seedlings may be obtained. These figures we have called the hereditary percentages. I have been able to select the parent plants after their death on the sole ground of these values. And the result has been that from varieties which, on an average, exhibited 50-55% deviating seedlings, after one or two years of selection this proportion in the offspring was brought up to about 90% in most of the cases. _Phacelia_ and mercury with tricotylous seedlings, and the Russian sunflower with connate seed leaves, may be cited as instances.

Besides these tests, others were performed, based only on the visible characters of the seedlings. The result was that this characteristic was almost useless as a criterion. The atavists gave, in the main, nearly the same hereditary percentages as the tricotyls and syncotyls, and [821] their extremes were in each case far better constituted than the average of the chosen type. Hence, for selection purposes, the atavists must be considered to be in no way inferior to the typical specimens.

If it had been possible to apply this principle to twisted and fasciated plants, and perhaps even to other monstrosities, I think that it will readily be granted that the chance of bringing even these races up to a percentage of 90% would have been large enough. But the large size of the cultures required for the counting of numerous groups of offspring in the adult state has deterred me from making such trials. Recently however, I have discovered a species, _Viscaria oculata_ which allows of counting twisted specimens in the pans, and I may soon be able to obtain proofs of this assertion. The validity of the hereditary percentage as a standard of selection has, within the last few years, been recognized and defended by two eminent breeders, W.A. Hays in this country and Von Lochow in Germany. Both of them have started from the experience of breeders of domestic animals. Von Lochow applied the principle to rye. He first showed how fallacious the visible characters often are. For instance the size of the kernels is often dependent on their number in the head, and if this number is [822] reduced by the injurious varietal mark of lacunae (Luckigkeit), the whole harvest will rapidly deteriorate by the selection of the largest kernels from varieties which are not quite free from this hereditary deficiency.

In order to estimate the value of his rye plants, he gathers the seed of each one separately and sows them in rows. Each row corresponds to a parent plant and receives 200 or 150 seeds, according to the available quantity. In this way from 700 to 800 parent plants are tested yearly. Each row is harvested separately. The number of plants gives the average measure of resistance to frost, this being the only important cause of loss. Then the yield in grain and straw is determined and calculated, and other qualities are taken into consideration. Finally one or more groups stand prominent above all others and are chosen for the continuation of the race. All other groups are wholly excluded from the "elite," but among them the best groups and the very best individuals from lesser groups are considered adequate for further cultivation, in order to produce the commercial product of the race.

As a matter of fact the rye of Von Lochow is now one of the best varieties, and even surpasses the celebrated variety of Schlanstedt. It was only after obtaining proof of the validity [823] of his method that Von Lochow decided to give it to the public.

W.M. Hays has made experiments with wheat at the Minnesota Agricultural Experiment Station. He chose a hundred grains as a proper number for the appreciation of each parent plant, and hence has adopted the name of "centgener power" for the hereditary percentage.

The average of the hundred offspring is the standard to judge the parent by. Experience shows at once that this average is not at all proportional to the visible qualities of the parent. Hence the conclusion that the yield of the parent plant is a very uncertain indication of its value as a parent for the succeeding generation. Only the parents with the largest power in the centgener of offspring are chosen, while all others are wholly discarded. Afterwards the seeds of the chosen groups are propagated in the field until the required quantities of seed are obtained.

This centgener power, or breeding ability, is tested and compared for the various parent plants as to yield, grade, and percentage of nitrogenous content in the grain, and as to the ability of the plant to stand erect, resist rust, and other important qualities. It is evident that by this test of a hundred specimens a far better [824] and much more reliable determination can be made than on the ground of the minutest examination of one single plant. From this point of view the method of Hays commands attention. But the chief advantage lies in the fact that it is a direct proof of that which it is desired to prove, while the visible marks give only very indirect information.

Thus the results of the men of practice are in full accordance with those of theory and scientific experiment, and there can be little doubt that they open the way for a rapid and important improvement. Once attained, progress however, will be dependent on the selection principle, and the hereditary percentage, or centgener power or breeding ability, must be determined in each generation anew. Without this the race would soon regress to its former condition.

To return to our starting point, the comparison of artificial and natural selection. Here we are at once struck by the fact that it is hardly imaginable, how nature can make use of this principle. In some measure the members of the best centgener will manifestly be at an advantage, because they contain more fit specimens than the other groups. But the struggle for existence goes on between individuals, and not between groups of brethren against groups of [825] cousins. In every group the best adapted individuals will survive, and soon the breeding differences between the parents must vanish altogether. Manifestly they can, as a rule, have no lasting result on the issue of the struggle far existence.

If now we remember that in Darwin's time this principle, breeding ability, enjoyed a far more general appreciation than at present, and that Darwin must have given it full consideration, it becomes at once clear that this old, but recently revived principle, is not adequate to support the current comparison between artificial and natural selection.

In conclusion, summing up all our arguments, we may state that there is a broad analogy between breeding selection in the widest sense of the word, including variety testing, race improvement and the trial of the breeding ability on one side, and natural selection on the other. This analogy however, points to the importance of the selection between elementary species, and the very subordinate role of intraspecific selection in nature. It strongly supports our view of the origin of species by mutation instead of continuous selection. Or, to put it in the terms chosen lately by Mr. Arthur Harris in a friendly criticism of my views: "Natural selection may explain the survival [826] of the fittest, but it cannot explain the arrival of the fittest."

A

_Abies concolor fastigiata_, 618 _Acacia_, 176, 196, 217, 458, 697 bastard, 343, 617, 618, 664, 665, 666 _Acer compestre nanum_, 612 _Achillea millefolium_, 131, 132, 441 Adaptation, 702 double, 430, 451, 452, 454, 455, 457, 458, 642 _Aegilops ovata_, 265 _speltaeformis_, 265 _Agave vivipara_, 684 _Ageratum coeruleum_, 612 _Agrostemma Coronaries bicolor_, 125 _Githago_, 282 _nicaeensis_, 162 _Agrotis_, 204 Alder, cut-leaved, 147, 596 Alfalfa, 264 Algae, 699 Allen, Grant, 237 _Alliaria_, 638 _Alnus glutinosa laciniata_, 615 Alpine plants, 437, 695, 794 _Althaea_, 490 Amaranth, 282, 452 _Amaranthus caudatus_, 282 _Amaryllis_, 272, 275, 762 brasiliensis_, 275 leopoldi_, 275 pardina_, 275 psittacina_, 275 vittata_, 275 Amen-Hotep, 697 _Ampelopsis_, 239 _Amygdalus persica laevis_, 126 _Anagallis arvensis_, 162 _Androsace_, 634 _Anemone_, 266, 331 _coronaria_, 241, 491 var. "Bride," 510 _magellanica_, 266 _sylvestris_, 266 _Anemone_, garden, 241 Annee, 760 Anomalies, taxonomic, 658, 685 _Anthemis_, 236 _nobilis_, 130 _Anthurium scherzerianum_, 639 _Antirrhinum majus_, 315 _luteum rubro-striatum_, 315 Apetalous flowers, 622 Apples, 134, 240, 328, 454, 806 elementary species, 75 method of cultivating, 76 origin of cultivated varieties, 73 use by the Romans, 74 "Wealthy," 78, 79 wild, 73, 74, 75, 76 _Aquilegia chrysantha_, 161 _Arabis ciliata glabrata_ _hirsuta glaberrima_, 126 _Aralia crassifolia_, 662 Arbres fruitiers ou Pomonomie belge, 76 _Aralia papyrifera_, 662 Arctic flora, 695 _Arnica_, 494 _montana_, 236 Aroids, 222, 631, 639 Artemisias, 131 Artificial selection, 18, 71, 77, 93, 95, 743, 744, 798, 826 first employed, 72, 92 nature of, 19 _Arum maculatum immaculatum_, 125 Ascidia, 310, 366, 367, 427, 428, 669, 670, 671, 672, 673, 674, 675 Ash, 135, 341 one-bladed, 666, 667 weeping, 196, 596 Ashe, 343 Aster, 132, 152, 242 seashore, 200, 282 _Aster Tripolium_, 132, 200, 236, 282, 410 _Astragalus alpinus_, 696 Atavism, 154, 170, 172, 175, 176, 178, 182, 185, 187, 188, 198, 220, 222, 226, 235, 344, 354, 399, 405, 411, 660, 661 bud, 183, 226 definition of, 170, 631 false, 185, 187 negative, 344 positive, 344 seed, 176 systematic, 174, 222, 630-657 Atavists, 156, 201 heredity of, 412 _Atropa Belladonna lutea_, 592 _Aubretia_, 241 _Avena fatua_, 100, 207 _Azalea_, 178, 322 _Azolla caroliniana_, 239

B

Babington, _Manual of British Botany_, 36, Bailey, 78, 306, 684 Balsams, 334 Bananas, 90, 134 Banyan, 244 Barberry, 133, 180 European, 270 purple, 596 _Barbarea vulgaris_, 427 Barley, 98, 105, 133, 203, 678, 679 "Nepaul," 203, 676, 677, 679, 681, 682 Bastard-acacia, 133, 136, 140 Bateson, 250 Bauhin, Caspar, 72, 610 Baumann, 618 Beans, 90, 152, 327, 727, 735 Bedstraw, 648 Beech, 133, 135, 242 cut-leaved, 179, 196, 616 laciniated, 196 oak-leaved, 595 purple, 196, 593, 595 Beeches, 427 fern-leaved, 147 Beets, 68, 72, 92, 93, 792, 796, 801, 815, 817, 818 Californian, 796 European, 796 forage, 71, 72, 791 salad, 71 Beet-sugar, 67, 68, 69, 70, 71, 109, 165, 717, 791, 807, 813, 814 _Begonia_, 218, 366, 509, 765 ever-flowering, 148 tuberous, 272 _clarkii_, 272 _davisii_, 272 _rosiflora_, 272 _sedeni_, 273 _semperflorens_, 133, 148, 620 _Begonia_ bulbous, 372 _veitchi_, 272 Behrens, 804 Belladonna, 145 _Bellis perennis_, 236 _perennis plena_, 195 Bentham, 237 Bentham & Hooker, _Handbook of British Flora_, 36 _Berberis_, 133, 180, 455 _ilicifolia_, 270 _vulgaris_, 270 Bertin, 596 _Berula angustifolia_, 457 Bessey, 660 _Beta maritima_, 69 _patula_, 69, 70 _vulgaris_, 69, 70 _Betula_, 132 Between-race, 358 Bewirkung, Theorie der directen (Nageli), 448 _Biastrepsis_, 402 _Bidens_, 131 _atropurpurea_, 131 _cernua_, 131, 158 _leucantha_, 131 _tripartite_, 131 Bilberries, 577 Bindweed, 41924 Binomium, of Newton, 767 Birch, 133, 243 cut-leaved, 596, 616 fastigiate, 618 fern-leaved, 179 _Bisoutella_, 282 _laevigata glabra_, 125 Bitter-sweet, 125 Blackberry, 268, 768 "Paradox," 769 Blue-bells, variation in, 54, 491, 577 Blueberries, 769 Blue-bottle, 499, 507, 509, 510 Blueflag, atavism of, 172 _Boehmeria_, 675 _bilboa_, 685 Bonnier, 439, 441, 442, 444, 451, 795 Boreau, 663 Brambles, 126, 127, 147, 239, 244, 245, 268, 740, 769, 663 _Brassica_, 244 Braun, 738 Braun and Schimper, 494 Bread-fruits, 90 Briot, 618 Britton and Brown's Flora, 162 Brooks, 711 Broom, 140 prickly, 217 Broom-rape, 220 _Broussonetia papyifera dissecta_, 616 _Brunella_, 146, 268 _vulgaris_, 577 _vulgaris alba_, 201 _Bryophyllum calycinum_, 218 Buckwheat, 452 Bud-variation, 750 Buds, adventitious, 218 Burbank, Luther, 57, 79, 116, 134, 268, 758, 768, 769, 784 Buttercup, 331, 357, 410, 725, 740 Asiatic, 241

C

Cabbages, 428, 684 atavism in, 638 origin of varieties, 621 Cactuses, 444 Cactus-dahlia, 625 _Calamintha Acinos_, 437, 452 Calamus root, 222 _Calendula officinalis_, 502 _Calliopsis tinctoria_, 195 _Calluna_, 146 _vulgaris_, 437, 577 _Caltha_, 490 _palustris_, 331 _Camelina_, 684 _Camellia_, 178, 323 _japonica_, 368 Camellias, 331 Camomile, 130, 132, 156, 366, 494, 503, 509, 512 _Campanula persicifolia_, 151, 234 _rotundifolia_, 437 Campion, 283, 302, 304 evening, 281 red, 238 _Canna_, 751, 759, 761 _indica_, 760 "Madame Crozy," 760, 761 _nepalensis_, 760 _warczewiczii_, 760 _Capsella Bursa-pastoris apetala_, 585 _heegeri_, 22, 582, 583, 684 _Carex_, 53 Carnation, 178, 241, 491 wheat-ear, 227 _Carpinus Betulus heterophylla_, 180 Carriere, 491, 596, 612, 806 Carrots, 806 Catch-fly, 419 Carboniferous period, 699 _Casuarina quadrivalvis_, 649 Cauliflowers, origin of, 621 Caumzet, 614 Causation, theory of direct, (Nageli), 448 Cedar, pyramidal, 618 Celandine, 147, 245, 280, 365 oak-leaved, 603, 610, 611 _Celosia_, 621 _Celosia cristata_, 327, 411 _Centaurea_, 242 Centgener power, 20, 822 _Centranthus macrosiphon_, 424 _Cephalotaxus_, 170, 226 _pedunculata fastigiata_, 169 Cereals, 105, 106, 107, 119, 801, 804 origin of cultivation, 104 Character-units, 632 Charlock, 424 _Cheiranthus_, 490 _Cheiri_, 370 _Cheiri gynantherus_, 371 _Chelidonium laciniatum_, 22, 609 _majus_, 147, 365, 600, 610, 611 _majus foliis quernis_, 610 Cherries, 79 Cherry, bird's, 617 Chestnuts, 427 Chromosomes, 306 _Chrysanthemum_, 178, 274 corn, 739 _Chrysanthemum carinatum_, 494 _coronarium_, 161, 202, 510 _grandiflorum_, 739 _imbricatum_, 494 _indicum_, 490 _inodorum_, 503 _inodorum plenissimum_, 336 new double, 501 _segetum_, 202, 493, 504, 729 _segetum_, var. _grandiflorum_, 43, 495, 498, 504, 504 _Chrysopogon montanus_, 450 Cieslar, 804 _Cineraria cruenta_, 514 Cinquefoil, 52 _Clarkia_, 420 _elegans_, 198 _pulchella_, 282 _pulchella carnea_, 162 _Clematis Vitalba_, 662 _Viticella nana_, 612 Clover, 80, 102, 674 crimson (Italian), 353, 358, 359, 360 five-leaved, 340, 362, 374, 431, 509, 789 four-leaved, 340, 346, 352 red, 235, 281 white, 133, 366 Clusius, 610 _Cochlearia anglica_, 52 _danica_, 52 _officinalis_, 52 Coconut, 67, 82, 83, 87, 88, 89 dispersal of, 85, 89 geographic origin of, 88,89 Coconut-palm, 84, 88 Cockerell, T.D.A., 139, 140, 591 Cocklebur, 139 Cockscomb, 165, 327, 356, 411, 621 _Cocos nucifera stupposa_, 83, 84 _cupuliformis_, 82 _rutila_, 82 _Codiaeum appendicularum_, 673 _Colchicum_, 490 _Coleus_, 132 Columbine, 725 yellow, 161 Columbus, 89, 118 Columella, 106 Composites, 130, 131, 336, 723, 778 Conifers, 168, 226, 239, 455 weeping, 617 Connation, of petals, 660, 661 "Conquests," 242 Contra-selection, 425 Cook, 84, 86, 88, 89 Corn, 81, 90, 118, 119, 135, 283, 287, 288, 775, 786, 788, 804 American, 205 Corn-cockle, 162 Corn-chrysanthemum, 739 Corn-flowers, 491, 92 Corn, "Forty-day," 118 "Harlequin," 327 sterile variety of, 622 sugar, 135, 158 "Tuscarora," 205 Corn-marigold, 493, 494 Cornel berry, yellow, 196 Cornaceae, 675 _Cornu_, 338 _Cornus Mas_, 196 Correlation, 142 _Corylus_, 133 _Avellana_, 181 _tubulosa_, 181 Cotton, 725 Cotyledon, 674 variation in, 416 _Crambe maritima_, 621 Cranesbill, 599 European, 628 meadow, 322 _Crataegus_, 196 _oxyacantha_, 132 Crowfoot, 331 corn, 283 _Crepis biennis_, 410, 411 Cress, Indian, 192 Crosses bisexual, 255, 276, 294, 298 reciprocal, 279 unisexual, 255, 261 varietal (see Hybrids) _Croton_, 673, 674 Crozy, 760, 762 Crucifers, 222, 635 _Cryptomeria_, 169, 226 _japonica_, 239 Cucumbers, 118 _Cucumis_, 52 _Cucurbita_, 52 Cultivated plants, 65, 66 elementary species of, 62 improvement of, 92 mixed nature of, 96, 118 origin of, 91 Currants, 79 Californian, 270 flowering, 166 "Gordon's," 270 Missouri, 270 white, 158 white-flowered, 167 Cuttings, 721 _Cyclamen_, 323, 355, 627, 684 Butterfly, 627 _vernum_, 619 _Cypripedium caudatum_, 487 _Cytisus adami_, 271 _candicans Attleyanus_, 367 _Laburnum_, 271 _prostratus_, 139 _prostratus ciliata_, 125 _purpureus_, 271 _spinescens_, 139

D

_Dahlia_, 131, 241, 272, 625
cactus, 625
"Jules Chretien," 628
purple-leaved, 626
"surprise," 230
tubular, 627
[sic] 274, 490, 764
first double ones, 490
green, 227, 229, 230
Daisies, 131, 132, 494
double, 195
hen-and-chicken, 514
ox-eye, 202
Shasta, 769
yellow, 202
Dandelion, 411
parthenogenesis, 61
variations in, 60
Daphne Mezereum, 146
Darwin, 1, 2, 3, 4, 5, 6, 7, 18, 76, 85, 93, 109,
110, 180, 196, 205, 206, 242, 306, 324, 338,
448, 571, 604, 612, 689, 702, 710, 715, 743,
798, 825
Darwin, George, 711
Darwinian theory, 461
basis of, 5
Date, 134
_Datura Stramonium_, 139, 142
_Stramonium inermis_, 300
_Tatula_, 139, 142, 300
Dead-nettle, 237
De Bary, 38, 47, 49
De Candolle, 76, 84, 85, 89, 228, 370, 403, 621
Alphonse, 74, 129, 226
A.P., 129
Casimir, 659, 676
De Graaff, 275
_Delphinium Ajacis_, 192
Deniau, 617
Descent, theory of, 690, 694, 702, 707, 716, 798
De Serres, Olivier, 72
_Desmodium gyrans_, 655, 656, 663, 664, 65
Dewberry, California, 269
_Dianthus barbatus_, 322, 648
twisted variety, 408
Diatoms, 699
Dictoyledons
ancestors of monocotyledons, 15
_Digitalis parviflora_, 161, 640
_purpurea_, 483
pelorism of, 482
Dimorphism, 445, 447, 454, 457, 458
Dippe, 810
_Dipsacus fullonum_, 402
sylvestris_, 402, 402
Dominant character, 280
Double flowers
poppies 490
production of, 489
types of, 330
Double races (see also ever-sporting varieties),
419, 427, 428
Dubois, Eugene, 712
Duchesne, 185, 188, 596
Duckweed, 222
_Draba_, 692, 693
verna, 47, 50, 51, 53, 125, 126, 518, 533,
546, 547, 561
_Dracocephalum moldavicum_, 419
Dragon-head, 419
_Drosera anglica_, 268
_filiformis_, 268
_intermedia_, 268
_obovata_, 267
_rotundifolia_, 268

E

Earth, age of, 710
Edelweiss, 438
Eichler, 660
Election, 801
Electric light, growth in, 442
Elementary species, 11, 13, 32, 67, 74, 76, 77,
78, 79, 91, 95, 116, 119, 124, 126, 128, 129,
207, 238, 252, 256, 307, 430, 435, 695, 696,
698, 702, 715, 787, 798, 800, 825
apples, 75
coconut, 82
corn, 81
cultivated plants, 62
definition of, 12, 35, 127
flax, 80
how produced, 16, 248
hybrids of, 253, 255
mutation of, 141
origin of, 459, 603
origin of, how studied, 463
selection of, 92
varieties vs., 14, 15, 141, 152, 224, 243,
247, 251, 495
Elm, 136, 219, 239, 427
_Epilobium_, 268
_hirsutum_, 683
_hirsutum cruciatum_, 588
_montanum_, 269
_tetragonum_, 269
_Equisetum Telmateja_, 642, 649
_Erica Tetralix_, 577, 661
Ericaceae, 146, 660
_Erigeron _Asteroides_, 450
_canadensis_, 132, 236, 453, 600, 695
_Erodium_, 146
_cicutarium album_, 161
_Erucastrum_, 630, 638, 639
_pollichii_, 222, 637
_Eryngium campestre_, 674
_maritimum_, 674
_Erysimum cheiranthoides_, 638
_Erythraea pulchella_, 452
_Erythrina_, 621
_Crista-galli_, 620
Eschcholtzias, 59
Esimpler, 337
_Eucalyptus citriodora_, 669
_Globulus_, 217
_Euphorbia Ipecacuanha_, 55
Evening-primrose, 62, 204, 256, 424, 686, 687,
688, 690, 691, 694, 695, 699, 702, 703,
705, 707, 708, 713, 747, 793
Evolution, 93, 685, 686, 689, 704, 707, 709,
710, 713, 718
degressive, 222, 223, 249
progression in, 630
progressive, 221, 222, 223, 248
regression in, 630
regressive, 221, 222; 223, 24
retrograde, 221, 631
Extremes, asexual multiplication of, 742, 769

F

Fabre, 265
_Fagus_, 133
_Fagus sylvatica pectinata_, 179
Fan, genealogical, 700
Fasciated stems, 409, 412
Ferns, 63
cristate, 427
plumose, 427
_Ficaria_, 53
_Ficus radicans_, 436
_religiosus_, 244
_repens_, 436
_stipulata_, 436
_ulmifolia_, 436
Figs, 436
_Filago_, 52
Fir, 134, 804
Fittest, survival of, 826
Flax, 80, 805
springing, 80
threshing, 80
white-flowered, 158, 160
Fleabane, Canada, 132, 236
Flowers, gamopetalous, 660
Fluctuability
embryonic, see Fluctuation, individual
Fluctuation, 708, 715, 716, 718, 719, 724, 737, 741
curves of, 729, 794
defined, 191
individual, 718, 723, 732, 741, 745, 749, 788
mutation vs. 7, 16, 719
partial, 718, 723, 732, 741, 745, 748, 749,
771
inadequate for evolution, in elementary species,
19
nature of, 18
specific and varietal characters vs. 17
Forget-me-not, 368
Fothergill, John, 521
Foxglove, 163
peloric, 164, 356, 367
yellow, 161, 640
_Fraxinus excelsior monophylla_, 667
_exheterophylla_, 667
_simplici folio_, 667
French flora (Grenier and Godron), 433
Fries
on _Hieracium_, 60
Frostweed, 440
species of, 52
_Fuchsia_, 272, 355
Fuchsias, 491

G

Gaertner, 279 _Galeopsis Ladanum canescens_, 139 _Galium_, 648 _Aparine_, 409, 648 _elatum_, 52 _erectum_, 52 _Mollugo_, 62 _verum_, 648 Gallesio, 138 Galton, 736, 776 Gamopetaly, 662 Garden-pansy, origin of, 38 Garlic, 638 Gauchery, 452 Geikie, 711 Genera artificial character of, 36 polymorphous, 692 _Gentiana punctata concolor_, 125 Gentians, 577 Georgics (Vergil), 106 _Geranium pratense_, 323, 628 _album_, 628 _pyreniacum_, 599 German flora (Koth), 432 Geum, 282 Gherkins, 118 Gideon, Peter M., 78 Glacial period, 696 _Gladiolus_, 241, 272, 274, 368, 765 _cardinalis_, 275 _gandavensis_, 275 _psittacinus_, 275 _purpureo-auratus_, 275 _Glaucium_, 241 _Gleditschia sinensis_, 614 _triacanthos pendula_, 617 _Gloxinia_, 282, 485 erect, 626 _Gloxinia erecta_, 485 peloric variety, 485 _Gnaphalium Leontopodium_, 438 _Godetia amoena_, 161 Godetias, 59, 232 Godron, 265, 432 Goeppert, 370 Gooseberry, 79, 140, 626 red, 133, 165, 241 Grapes, 90, 158, 328 Grape-hyacinth, _plumosa_, 134 Grasses, 102, 631, 681 Grenier, 433 Groundsel, 132 Growth, nutrition and, 714, 720, 722 Guelder-rose, 134, 239 Gum-tree, Australian, 217 _Gypsophila paniculata_ twisted variety, 409

H

Haeckel, 707 Half-races, 358, 372, 409, 419, 424, 427, 428 Hall, 444 Hallet, F.F., 109 Harebell, 232 peach-leaved, 234 Harris, Arthur, 825 Harshberger, John W., 591 on _Euphorbia_ in New Jersey, 55 Hawksbeard, 410, 411, 412 Hawkweed, 411, 439, 443, 819 Hawkweeds seeding without fertilization, 61 Hawthorn, white, 132 Hays, W.M. on individual selection, 20, 94, 95, 117, 821, 823, 824 Hazelnut, 133, 181, 242 Hazels, cut-leaved, 596,-616 Heath family, 146, 222, 660 Heaths, origin of, 662 Heather, 577 _Hedera Helix arborea_, 437 Hedgehog burweed, 140 _Hedys_Arum_, 664 Heeger, 582 Heer, Oswald, 74, 105 Heinricher, 172, 173, 174 _Helianthemum_, 53, 125, 126, 561 _apenninum_, 52 _pilosum_, 52 _polifolium_, 52 _pulverulentum_, 52 _vulgare_, 440 _Helichrysum_, 420 _Helwingia_, 678, 678, 682 _rusciflora_, 675 Hemp, 419 Henbane, 282 _Hepatica_, 322, 490 Heredity, 731, 734, 818 bearers of, 632 in teasels, 642 _Hesperis_, 241, 322 _matronalis_, 323, 411 _Heylandia latebrosa_, 450 _Hibiscus Moscheutos_, 591 _Hieracium_, 59, 439 _alpinum_, 696 Hildebrand, 160, 240, 241 Hoffman, 160, 662 Hofmeister, 160, 370, 480 Holbein, 164, 596 Holly, 140, 196 Holtermann, 449, 451 Hollyhock, 427 Honeysuckle, 674 ground, 443 _Hordeum distichum_, 677 _hexastichum_, 677, 678 _tetrastichum_, 677 _trifurcatum_, 676, 678 _vulgare trifurcatum_, 203 Hornbeam, European, 180 Horse-chestnut, 219 thornless, 234 Horsetail, Canadian, 695 European, 649 Horsetail, family, 641 Horse-weed, 132 Canadian, 452 _Hortensia_, 134, 181 Horticulture, mutations in, 604 Houseleek, 370, 371 Hunneman, John, 521 Hyacinths, 178, 322 white, 160 Hybrids, 58, 201, 202, 206, 250, 575 between elementary species, 253 constant, 263, 264, 265, 266, 267, 268, 269 law of varietal, 716 Mendelian, 324 nature of, 20 species, 256, 260 splitting of, 210 varietal, 208, 209, 247, 277, 278, 279, 281, 285, 293, 294 Hybridization, 706, 751, 752, 758, 759, 764 _Hydrocotyle_, 668 _Hyoscyamus niger_, 282 _pallidus_, 283 _Hypericum perforatum_, 725 _Hyssopus officinalis_, 161

I

_Iberis umbellata rosea_, 195 Improved races, inconstancy of 770-797 Indian cress, 668 pelorism of, 485 Indian pipe, 661 Ipecac spurge, 55 _Iris_, 456 _falcifolis_, 172 _kaempferi_, 174 _lortetii_, 521 _pallida_, 172 _pallida abavia_, 681 Isolation, 108 Ivy, 436

J

Jacob's ladder, 200, 202 Jacques, 614 Jacquin, 52, 632 Jaggi, 594, 595 Jaeger, 228, 662 Jalappa, 165 Janczewski, 266 Japanese plum, 58 _Jasminum Sambac_, 662 Joly, 712 Jordan, Alexis, 45, 47, 49, 50, 129 experiments with species, 37, 40 _Juncus effusus spiralis_, 684 Juniper, 684

K

Kapteyn, 716 Kelvin, Lord, 720, 711 Kerner von Marilaun, 266, 267 Keteleer, 618 Knight, 390, 719, 720 Koch, 433, 667 Koelreuter, 279 Korshinsky, 609, 612, 614, 617, 667 Krelage, 510, 619 Kuhn & Co., Messrs., 801, 809, 817

L