« PreviousContinue »
albino partner are in turn mated. Two black guinea pigs are presumably as surprised as a hen that has hatched ducklings by the appearance of one white guinea pig for about every three black ones in the family circle. The original cross had brought together two characteristics, B (black) and W (white), to make a single individual, BW, which showed only the dominant black characteristic. When these individual B Ws formed germ cells for the continuation of their species there was a return to original conditions ; B became the sole characteristic of some of these germ cells and W the sole characteristic of others. When these germ cells united to create a new individual there were necessarily three possible combinations—B B, B W, and WW, the combination BW evidently occurring twice as often as either of the
miss methods of fancy breeding, and England has "mice clubs” whose members, just for the fun of it, have long been interested in obtaining fancy house mice with pink eves and variously colored overcoats instead of the uniform gray costume of the usual victim of the
me of the usual victim of the domestic mouse trap.
All these differences, secured apparently by chance but really, it nowy appears, in obedience to a law of heredity, are of direct value in still further testing the uniformity of the law and in getting new lines on the problems of inheritance. In this scientific menagerie the guinea pigs, rabbits, rats, and mice include specimens of practically all the varieties yet produced by experimental breeding.
Each has a pedigree, so far back as it · can be traced, neatly recorded in a card catalogue, and, as the experiments inspire no fear or distrust of their keepers, they are most of them tame and easy to handle. The rabbits in particular behave
Johnny's coop in a suburban back yard.
A typical working out of the Mendelian law of heredity may be seen in the mating of an albino and a black guinea pig. If a pure bred black guinea pig is mated with a white one all the young guinea pigs in the first litter are black. These baby pigs are apparently the offspring of black parents, although, as a matter of fact, the white parent has contributed something of her own color characteristic and the contribution is unseen because the black color characteristic is dominant and conceals it. According to the Mendelian law the white color characteristic, being recessive, can appear visibly only from the union of two germ cells in both of which this characteristic predominates—and that is exactly what happens when the black children of this black guinea pig with an
others. And, as any individual containing the dominant characteristic B would be black in color it follows that the combination W W would alone produce a white individual and would be likely to occur on an average of about once in four offspring. Evidently, too, in the case of individuals represented by BB and W W one characteristic had been doubled and the other eliminated.
By applying the Mendelian law in scientific breeding new combinations of individuals or races can be obtained in the course of a few generations. Thus when a guinea pig with a dark and smooth coat is mated with one whose coat is smooth and white, the young will exhibit a wholly new combination, dark and
ancestor ; that this tendency was recessive; and that it could only be perpetuated by union with another recessive tendency of the same kind, supplied in this case by the visibly four-toed father. Selective breeding among the descendants has since "fixed” the type so that it breeds true and adds yet another striking characteristic for the study of inheritance.
There are some characteristics, howrough and if these dark and rough ever, in which so far the Mendelian law guinea pigs are bred together a fourth
does not altogether coincide with the obcombination will appear in the grand served results of scientific breeding. alchildren of the original couple. Some of though it is now believed that further inthese grandchildren will be white and
children will be white and vestigation will discover another applicasmooth while others will represent the tion of the same principle. Size is the combinations seen respectively in the most important of these exceptions. parents and grandparents. By proper
Whereas color characteristics have been selection of parents any one of these proved to vary with predicable uniform, combinations may be established as a
ity, size is apparently a permanent blend pure race of guinea pigs in which the children will invariably resemble their father and mother. Often also a new combination of characteristics obtained through experimental crosses will coincide with some long lost racial combination. The yellow rabbit mated with a black one may produce a certain proportion of little rabbits with the characteristic gray color of the wild progenitors of both father and mother. In the same way occur presumably those occasional surprising cases in human families when PRODUCED BY MATING DESCENDANTS OF BLACK AND a son or daughter developes racial pecu
In their second generation the white color characteristic liarities not visible in either parent. If contributed by grandfather pig appears in the
estimated proportion. their genealogies could be carried back far enough each parent would probably be found to possess an ancestor of the of inheritances. In a typical rabbit famrace to which the child had reverted— ily the size of the offspring is intermediso, at any rate, we may deduce from the ate between that of the parents and none guinea pig.
of the descendants revert to the extreme A case of such reversion, for example, proportions of either grandparent. The has resulted in Dr. Castle's laboratory in practical result of this condition is that the evolution of a race of four-toed scientific breeding may produce at will a guinea pigs. The laboratory some years race of rabbits of any desired size beago came into possession of a male tween the known limits of size in rabbits, guinea pig whose four-toed feet made and with any conceivable combination of him unique among all the guinea pigs in color characteristics. The variation in the collection. There was no other like size is apparently continuous and depends him. And yet the four-toed guinea pig upon blending or striking a compromise one day surprised observers by becom- between the sizes of the parent rabbits. ing the father of a four-toed descendant. The variation in color depends upon the The mother was apparently normal. The scientific selection of parent rabbits in only explanation, therefore, was that she which the desired color characteristic is had inherited what might be called the not counteracted by any other. . four-toed tendency from some distant These transmitted characteristics, it
will be seen, are invariably associated being, and the thoughtful observer with the parent at birth and are never naturally wonders about subtler inherit"acquired” by the necessities of indi- ances than those of size and color. There vidual existence and then transmitted to is the question of inherited intelligence offspring. Dr. Castle's experiments, like and disposition—and this, in fact, is the those of many modern students of biol- next step in the study of the lower aniogy, tend to disprove the theory that ac- mals. Work is now in progress in Dr. quired characteristics can be transmitted. Castle's laboratory to investigate the efRather they confirm the conclusions of fects of a union between wild and tame Weissmann, which for twenty years have animals; the wild rat, for example, been the battle ground of biological opin- mated with a rat that has been domestiion, that the germ plasm, or reproductive cated by several generations of captivcells on which the continuity of all or- ity. These experiments are recent, but, ganic life depends, is independent of the so far as they have gone, they seem to body containing it, and that it is not influ- indicate that the strength and ferocity of enced by the characteristics acquired by the wild creature is the dominant charthat body during the space of a single life- acteristic according to the Mendelian time. This theory of inheritance casts an law. The offspring of the wild and the interesting and hopeful light on the sta- tame rat are in the first generation all tistics that are every now and then pub- apparently as wild as if they had been lished to show that the physical condition born of two wild parents, but when the of the average city-bred individual of offspring are mated the characteristics of today is inferior to that of his immediate the wild rat appear in modified form in ancestors. It would seem to indicate that some of the descendants while others such retrogression is not the result of in- seem to lack it entirely. These qualities heritance but of environment, and that are readily recognizable and the work of healthier living conditions in the large the psychologists with the various kinds cities, together with a wider distribution of apparatus they have invented for the of population back to the country, would study of intelligence in the lower anicounteract the tendency and produce a mals fortunately offers a means of excorresponding physical improvement. amination for mental characteristics that But it is also true, judging by these are more difficult to determine. The lower animals, that the statistics indicate psychological study of individual animals breeding from inferior family and racial and the psychological examination of stocks as a serious factor in the retro- their offspring and descendants for ingression of a startling number of indi- herited traits of intelligence is the next viduals.
step to be taken by these trained searchIt is still a far journey from guinea ers in the investigation of heredity by pig, mouse, rat or rabbit to a human scientific breeding.
APTAIN MAYNE REID, ture. Some of Mr. Meyer's experiences whose books have made nat- are akin to those of the three hunter uralists of more than one naturalists whom Captain Reid repreAmerican boy, once wrote a sented as having been sent out on like
story called, “The Plant errand by the authorities of the Kew Hunters." Its title was not particularly Gardens of London. alluring to the lads of the generation who The adventurous botanists of the old looked to their favorite for tales of pure tale were seeking specimens to be dried adventure, but before they had read long and preserved for museum purposes. they knew that they were to get excite- The adventurous botanist of the present ment with their botany.
tale cares nothing for the cut and dried. The heroes, there were three of them His is what David Fairchild of Washin the Captain's book, if memory's long ington, the Agricultural Explorer in shadow does not obscure the facts, were Charge of Foreign Seed and Plant Inon a plant hunting expedition in a valley troduction, calls “a living work." of the Himalaya Mountains. The scene I t is the duty of the man now in a of action was laid largely in wild places great desert of the Himalayan region to virtually geographically identical with secure seeds or cuttings of plants, shrubs those which are being searched today for and trees which he considers worthy of species of plant life by Frank N. Meyer, introduction into the United States, and an American field explorer working to get them quickly to Washington where under commission of the Bureau of Plant the work of propagation almost instantly Industry of the Department of Agricul- is started.
OUR WESTERN STATES.
to hide some design on the peace of the government or the community. The specimen bag must hold some strange instrument of destruction, the more deadly because it is unknown. The experiences of botanists in the Eastern mountains, though with an added element of real danger, are like those of the peaceful opera glass ornithologist whose sanity is doubted and whose arrest is threatened by the country folk because he prefers to study the living bird rather than to kill it, fill it with cotton
and arsenic, and to pierce Highly RECOMMENDED AS A SHADE TREE IN THE ARID REGIONS OF
it with wires for mounting
in painful and grotesque A drought-resistant species of poplar in Krasnawodsk, Turkestan.
Admittedly the expresExplorer Meyer is today in a lonelysion falls within the limits of what the land and before his mission is ended he objectors call the bromides, but it is the will pass through still lonelier lands. His desire of David Fairchild, the Agriculcollecting journey began at St. Peters- tural Explorer in Charge, and of his burg and it will end at some sea coast fellow laborers in field and Capital, to port of Eastern China. His trip already make such deserts as the United States has been successful enough to make it has to blossom like the rose or, if not the worth much more than the money it has rose, the pear, the apple, the orange, the cost. He has frozen and melted alter- pomegranate or the olive. The nature nately as the altitudes have changed; he has encountered wild beasts and men nearly as wild; he has scaled glaciers and crossed chasms of dizzying depthis; he has been the subject of the always alert suspicions of government officials and of strange peoples jealous of intrusions into their land—but he has found what he was sent for.
A plant hunter! Official and peasant are accustomed to the coming of hunters of wild beasts. They understand the lust of killing and the desire for danger which make men take long journeys into strange places. But a plant hunter !-It seems to them the thinnest pretense