way and avoids some difficulties of the simpler theory mentioned above, it is not to be considered as final.

waves, the method may be used to pick out waves of a certain length from a complex beam. Ives has studied the absorption of electric waves in ionized as compared with non-ionized air and water vapor and obtained results almost great enough to account for the difference between day and night transmission of wire

As regards the conduction of heat, the trend of opinion is undoubtedly back toward the earlier view that molecular motions are chiefly responsible for the conduction of heat through solids, and that the remarkable fact that many good conductors less waves. of electricity are also good conduc- X-Rays and Discharge Through tors of heat, is of secondary impor- Gases.-While some interesting work tance. One of the most puzzling on X-rays has been carried out, it is properties of metals is their so-called notable that American experimenters "contact electromotive force," which have not stepped into the new field shows itself in this way, that if two of X-ray diffraction and reflection by different metals are connected elec- crystalline and other solids. Since trically to earth and then brought Laue and Friederich's beautiful piowith two faces near each other, the neer experiments of 1912, a host of forcontiguous faces will at once become eign observers have taken up the work charged with electricity in a perfectly and at least the fundamental question definite way, which surface becomes seems to have been settled that positively charged depending on what X-rays are electromagnetic pulses of particular pair of metals is used. the same nature as light, but with Hennings (ibid., July, 1913, p. 1) has an effective wave length about carefully examined the problem and 1/10,000 that of the shortest known settled some disputed points; for ex- light wave. By a most refined study ample, he has shown that it depends of the effect of X-rays in breaking only on the surfaces which are close up air molecules into positively and to each other, and that either surface negatively charged ions, Plympton has charge will not appear if the one brought out the fact that for the first metal is screened by a wire gauze not one-third of a second after the ions too far away. The real cause of the are produced they are very likely to effect, whether due to an insulated elec- recombine because of their proximity; tric layer brought out by chemical ac- after this period the rate of recomtion or to a direct action of the surfaces bination becomes constant. The puzof the metals, is not known at pres- zling fact that X-rays and ultraent, though some results of Page and violet light when passed through a some observations of Millikan count thin film of metal drive off more decidedly against the layer theory. electrons from the metal in the direction in which the light (or X-rays) is going than in the opposite direction has been taken by some to indicate the necessity of returning to a corpuscular theory of light. Richardson and others have considered the matter from the standpoint of the electromagnetic-wave theory of light, and while the question is by no means settled it seems certain that the wave theory can be made to account for all the facts.

After several years of elaborate study of all possible sources of error, Millikan has published (ibid., August, 1913, p. 109) his final value of the elementary electrical charge or "atom" of electricity, as determined by his beautiful oil-drop method, namely, 4.774×10-10 electrostatic units. This in part depends on Gilchrist's new measurements of the viscosity of air, and is by all odds the most accurate determination of this very fundamental quantity.

Radioactivity.-While radioactivity Electric Waves.-Severinghause does not attract as many workers as and Nelms (ibid., June, 1913, p. 411) it did a few years ago, there is a have studied electric waves reflected steady increase in the knowledge of several times from screens of uniform the chemical properties of radioactive strips of metal (resonators) and have substances (McCoy and others) and shown that, like the corresponding in the knowledge of the various intercase of selective reflection of light mediate products of disintegration.

netized, the theories are still far from complete. An entirely different theory is that advocated by S. R. Williams, and though by its means he has been able to predict a number of magnetic effects, the theory seems essentially less valuable than that based on moving electrons. During the year Pierce (Proc. Am. Acad., Novem ber, 1913, p. 555) has continued his careful study of the magnetic prop

Of special importance is the study of the scattering, reflection, etc., of the various radioactive rays by matter, as this raises fundamental questions as to the structure of atoms. While the study of this scattering has led Rutherford to suggest that atoms consist of a small positively charged nucleus surrounded by electrons, interest has been added to the older hypothesis of Thomson by a paper of Crehore. He imitates the action of Thomson's erties of iron. The influence of a sphere of positive electricity through which electrons move, by proper use of the force of gravity, and obtains photographs of some artificial but possible atoms. An interesting paper by Bohr (Philos. Mag., Nov., 1913) is devoted to a detailed working out of a Rutherford type of atom. Bumstead has added greatly to our knowledge of rays, slow moving electrons sent off from metals which are struck by a rays (positively charged particles of atomic size). Duane has studied the motion in a magnetic field of ions produced by the heavy positive a rays from radium and has concluded that while the positive ions are molecules or atoms of nitrogen and oxygen, the negative ions seem to be always electrons. Wellisch has shown that there is a definite limit to the percentage amount of active material which will be deposited on a negatively charged electrode exposed to radium emanation, the remaining active material losing its charge almost as it is formed. Work of Gray on the scattering of X and y rays indicates that there is probably very little real scattering of these rays when they pass through matter, but rather a reradiation.

magnetic field upon either the emission or transmission of light (Zeeman and Kerr effects) has been the subject of much recent experimentation and extensive theoretical work, the latter by Voigt especially. While all work up to 1913 has shown that light emitted in a magnetic field was more complex, that is, contained more different wave lengths than light from the same source not in a magnetic field, the use of stronger magnetie fields has now brought out the unexpected fact that a very strong field simplifies the light emitted, that is, reduces the number of different wave lengths. Voigt has been able to modify his theory to account for this. As regards the passage of light through a magnetic field, or reflection from the polished pole of a magnet, C. Snow has successfully applied Voigt's theory to account in a most exact way for the observations of Ingersoll.

Conclusion.-While the year 1913 has not been remarkable for any great or fundamental contribution to physical knowledge or theory, nevertheless a large amount of good work has been done, especially in the way of careful experimental testing of hy potheses. The most noticeable thing Magnetism. The relatively small is the continued almost unquestioned amount of work done in this field acceptance of the revolutionary idea does not indicate that all the puz- of Planck, referred to under "Eleczling questions are answered, but tricity," that energy is emitted from rather, perhaps, a difficulty in con- radiating bodies in lumps or bundles, necting experiment with theory as the to put it crudely. In Science of Jan. latter now stands. Williams has pub- 24, 1913, will be found an excellent lished an interesting compilation of summary by Millikan of the current the various attempts to form an elec- attitude toward this idea of Planck, tronic theory of magnetism by Weiss, which has influenced every branch of Langevin, and others. While doubt physics, and in Science for Sept. 19 less in the main correct in ascribing and 25, 1913, the more general adthe magnetic properties of molecules dress of Lodge, in which the ideas of iron, etc., to the presence of elec- of continuity versus discontinuity are trons moving in orbits, which turn considered from a much more general and face one way when a bar is mag-point of view.

XXVII. THE BIOLOGICAL SCIENCES

ORGANIC EVOLUTION

W. L. TOWER and JOHN G. SINCLAIR

environmental control as it is practiced in Vienna is given in detail by Pzibram (Zeitschr. biol. Tecknik u. Methodik, III, 163-245). While employing material ostensibly of solely agricultural interest, the investigators in our agricultural experiment stations are in many cases dealing with strictly scientific as well as economic problems.

General Survey of Activities.-The center of interest in problems of organic evolution during the year lies in three phases of heredity: the role of sex in inheritance, the behavior of hybrid characters, and the experimental modification of inheritance. Morgan in his recent book, Heredity and Sex (Columbia University Press), treats this heretofore bewildering mass of data simply and clearly. The view Adaptation. The interpretation of taken is a welcome aid to further natural phenomena received contribuwork even if incomplete. The work in tions from several sources during the heredity previous to 1913 is reviewed year. The decadent subject of mimicritically by Plate in the Vererbungs- cry and protective coloration is relehre (Leipzig, 1912). Both these vived on a somewhat more critical books contain excellent bibliographies. basis by Jacobi (Die Wissenschaft, Modification of inheritance is the most recent phase of the evolution problem and its treatment is fragmentary.

The extent of investigations may be indicated by a few specific cases. Few investigators are in a position to carry out really critical experiments with incident forces. The University of Chicago has met the difficulty of conducting intensive research in evolution by more than doubling the capacity and equipment of its experimental plant; environmental control is a feature of this laboratory. The natural climatic complex at the Desert Botanical Laboratory in Tucson, Ariz., permits the conduct of mass experiments to compare with those at Chicago. At Cold Spring Harbor the collection of critical data on human inheritance is an important feature. New laboratories are being opened in England and on the Continent, prominent among which is the new Imperial Institute in Berlin; many good workers are preparing for an active investigation of heredity in this laboratory. The mechanics of

XLVII). Adaptations of all sorts experienced a thoroughly mechanistic interpretation at the hands of Metcalf, Livingston, Henderson, Parker and Mathews in a "Symposium on Adaptation" (Am. Nat., XLVII, 65-116). They reflect well the attitude of present experimental biology. No other science has so long retained its teleological terminology as has biology, and it is refreshing to note the change in the type of investigations toward quantitative, analytic and synthetic work. A good working knowledge of the physical and mathematical sciences is becoming yearly more necessary in biological laboratories. Henderson's book, The Fitness of the Environment, presents the interacting system of the organism and its medium from this point of view. Verworn in his last edition of the General Physiology and again in his lectures on Irritability (Yale University Press, 1913) attacks the idea of causal factors in biological phenomena, noting the fact that any necessary condition to a reaction may be considered its

cause if it is so desired. Shelford | Morgan (Am. Nat., XLVII, 5-16) had applies the same idea to out of door a race of wingless flies among which nature (Animal Communities, Uni- one appeared with one wing. The race versity of Chicago Press, 1913). Any mutated from the normal wild fruit environmental factor may become a fly apparently by loss of a factor for limiting factor for any organism ef- wings. This case is offered as argument fecting either its response or its very against the presence-absence hypothexistence. Animal communities physi- esis of unit characters in favor of a ologically equivalent are thus main- simple readjustment of the germinal tained. This affords to some degree complex. Heribert-Nilsson (Zeitschr. an explanation of geographical dis- ind. Abst. Vererb., VIII, 90-231) tribution as well as of local associa- has studied the variations of some tions. pure lines of Oenothera lamarckiana, and obtained inheritable variants of all the characters which constitute the famous work of De Vries. Some were not so intense as these mutants and various gradations down to the normal were present. He claims that combinations of these variations give the mutant forms. That the synthesis of mutating stem stocks and fixed hybrids occurs in nature is open to little doubt. The importance of this phenomenon in evolution is debatable and a fit subject for experimental work. At present the origin of new species other than recombinations does not result from them. Better methods of studying variations disclose more mutations yearly. New types reported are: Safir for Drosophila (Biol. Centr., XXXII, 47-54), Kiessling for barley (Zeitschr. ind. Abst. Vererb., VIII, 48-78), and for the negro Castle and Simpson (Am. Nat., XLVII, 50-7).

Cytology. The material basis of heredity continues to be a study largely of chromosomes, particular attention being paid to sexual differences of chromosome number. Wilson presents the study of "Heredity and Microscopic Research" (Science, XXXVII, 961) in a fairly dogmatic manner, pointing to the complete correlation of data from the field of cytology and breeding. Special studies of the Xchromosome in distinguishing sex and its linked characters are the subject of part of Morgan's Heredity and Scx, and of several articles. Sturtevant (Jour. Exper. Zool., XIV, 43-61) has formulated the lineal arrangement of hereditary factors along specific chromosomes of Drosophila, while Bridges (ibid., XV, 587-606) tries to explain a variation from the expected ratio in a case of sex linkage by reference to non-disjunction of the female Xchromosomes at maturation. Several studies on the chromosome complex in hybrids, the parent chromosomes being diverse, give the expected arrangement, and serve as a possible explanation of sterility or failure in development. It is, however, very difficult to evaluate the cytological evidence for heredity. That it confirms or helps to explain the data of breeding is quite true. Whether it will ever form the basis of predictions to experiment or will serve to open up new phases of breeding investigation is questionable.

Variation. Mutation.-The necessity of "pure stock" is almost a truism among breeders, though the difficulty of a criterion for purity is apparent to those who study variation carefully. The chapter on meristic variations in Bateson's Problems of Genetics (Yale University Press, 1913) is worth noting in this connection.

Inbreeding and Crossbreeding.-The effects of inbreeding are still debatable. Shull (Biol. Bull., XIV) gets degenerative effects in rotifers. Long continued experiments on protozoa, flies, beetles, and mammals show an inappreciable effect, except as inheritable weaknesses in both parents tend to become more fixed in the offspring. Calkins and Gregory in studying the later history of the progeny of exconjugants in Paramecium (Jour. Exper. Zool., XV, 467-527) find that each one is not a potential germ cell and therefore immortal as Weissman stated. Some die soon, some continue indefinitely without further conjuga tion, and to others periodic conjugation seems necessary to continued life. Jennings and Lashley (Jour. Exper. Zool., XIV, 393-466) find biparental inheritance of vigor and productivity among these forms. Crossbreeding undoubtedly invigorates a stock in

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most cases. Practical breeders like of hair and eye color (Brownlee, Proc. Webber, Marshall, and Anderson (Am. Roy. Soc. Edin., XXXII) have been Breeders' Mag., III), and Nilsson- discussed during the year. Rogers Ehle (Conf. int. de Genetique, IV) (Am. Breeders' Mag., III) has prestate that the main advances in all sented an extensive table of geneallines of practical breeding have been ogies of the feebleminded. (See also through hybridization and extraction. XVI, Eugenics.) An extensive investigation of the histological as well as apparent inherited characters of hybrid plants shows intermediate forms in 100 of the 121 characters tabulated (H. B. Brown, Miss. Agr. Exper. Sta., Tech. Bull., 3). It is found possible to state the degree of dominance quantitatively. The production of sterile hybrid stock may be avoided by the dilution of one strain in breeding back, if Detlefsen's results (Am. Breeders' Mag., III) are of general application. In crosses of wild and domestic guinea pigs, what he calls one-eighth wild hybrids were fertile. That increasc variability results from hybridizing ducks is shown by Philips (Jour. Exper. Zool., XII). The same result is not obtained through conjugation in Paramecium. Davis (Am. Nat., XLVII, 449-77, 54064), while reporting progress in the hybrid synthesis of O. lamarckiana, has not yet produced a "mutating stem form." Mendelian principles have been successfully applied by Emerson and East to quantitative characters in maize (Neb. Agr. Exper. Sta. Bull. 2). Gametic coupling, with or without sex, forms at present an intricate chapter in breeding. Vilmorin (Jour. of Genetics, III, 67) reports that certain dwarf mutants in wheat while dominant to the normal can never be extracted pure, always giving 20 to 30 per cent. of tall progeny. In the researches of Tanaka (Jour. Coll. Agr. Tohohu Imperial Univ. Japan, V) and Toyama (Biol. Centr., XXXII) certain dominant characters of the silkworm show complete coupling or repulsion in the hybrids, depending on whether they are introduced through one or both parents.

Determination of Dominance and | Sex.-Dominance is reported by Cook to be to some extent regulated externally in cotton breeding (Bur. Plant Ind. Bull. 256). It is, moreover, not constant in corn, where an albino mutant of yellow dent was at first dominant to yellow, later becoming recessive (Collins, Bur. Plant. Ind. Bull. 272). Richard Hertwig and Kuschakewitch have revived the question of sex determination (Biol. Centr., XXXII). By preventing female frogs from laying their eggs for two or three days after the normal period, the percentage of males in the offspring was increased in some cases to 100 per cent., the normal ratio being one to one. Differential mortality does not explain the result when the total mortality is only five per cent. It is suggested that delayed fertilization renders the egg nucleus unfit for further development. Fertilization then starts a parthenogenetic cycle in which the sperm nucleus alone takes the part of the usual double nucleus. This criticism demands further test. cattle breeding Pearl and Parshley report similar but less marked phenomena when coitus occurs late in the œstral period (Biol. Bull., XXIV).

In

Experimental Evolution.-The question of the inheritance of acquired characters and the direct modification of germinal constitution have in practice become so closely allied that distinctions are purely academic. Sumner has produced modified forms in mice through the action of external temperatures, which persisted in inheritance. Now (Jour. Exper. Zoöl., XV, 315-79) he finds that internal temperaEugenics consists at present largely tures of the mice are not disturbed of the study of human hybrids. Shus- by change of external temperatures ter has written a simple and general beyond the individual fluctuations of text on Eugenics (Oxford University the mice. Thus he believes the influPress), taking the stand that enough ence upon the germ plasm came indiis known to warrant taking positive rectly through the soma. The salasteps in applying eugenic principles. mander is polymorphic with regard Traits of character (Woods, Am. to color. Kammerer (Entw. Mech.. Breeders' Mag., III) and the coupling XXXVI) studies the effect of dry and