general laws of human energetics, have been long established. But details which are of great importance when any exact view of the subject is desired, still escape us. To express the energy requirements of agricultural laborers in terms of food with the precision attainable by an actuary in estimating their average expectation of life is still an ideal of the remote future. This is only in part due to the greater difficulty of measuring energy transformations as compared with the measurement of longevity. It is now quite possible by means of relatively simple apparatus to carry out such determinations on a large scale. But the task is not one that any private investigators can be expected to undertake. The mere compilation of statistics of family consumption, a less laborious affair, occupied much of the time of the United States food investigators for years. Here is a proper object for the team work of which so much is heard in these times. It involves physiological skill both in making the measurements themselves and in paying due heed to the attendant circumstances, such as the cooling power of the air in the factory or workshop, a point scarcely heeded by many past students; industrial knowledge is needed to decide what factory processes are in pari materia so that representative samples may be chosen for experiment; lastly, some experience in the handling of numerical data is required to decide the significance of departures from the average and the limits of precision of the averages themselves. Nor does it suffice to enroll a suitable team of investigators and send them out into the factories to collect data. The routine application of a physiological technique is the death of science. When a method is intelligently applied upon a large scale anomalous results must emerge, the analysis of which upon a laboratory scale and with the attendant simplification of the conditions may lead to the discovery of new and important truths. The investigating staff must be attached to a headquarters laboratory controlled by a physiologist competent to sift real anomalies from mere technical errors and to cause them to be

sedulously investigated. We conceive that in this way alone a really adequate knowledge of the energy requirements of muscular work can be attained.

When it is remembered that this problem, important as it is, is only one of the problems of human nutrition which are still unsolved, we do not think more need be said in support of a national laboratory of nutrition. No doubt the time will come when the intelligent citizen will find it difficult to understand how any nation could neglect to make such a provision for its literally vital needs.-British Medical Journal.

SCIENTIFIC BOOKS

An Outline of the History of Phytopathology. By HERBERT HICE WHETZEL. Philadelphia and London, W. B. Saunders Company. 1918. Pp. 130, with 22 portraits.

The domain of plant pathology is rapidly taking shape as a highly important part of the contribution of botany to the economic life of the world, as well as a department of botanical science demanding recognition from students of the modern aspects of science in general. The enormous losses which crops suffer from parasitic and predatory fungi have long been recognized in a general way, but only in recent years, since numerous investigators have undertaken to study the causes which inhibit the optimum development of cultivated plants, has the great diversity in the etiology of plant diseases been so clearly shown. With the recognition of the diseases and their causes has grown up practical means for controlling or avoiding many of them. The economic returns have reacted upon the opportunities for investigation, and consequently great progress has been made in this department of botany within the few decades just past, more especially in America. The epidemic of the chestnut blight, the fight against the white pine blister-rust, the barberry-wheat campaign, and the government and state quarantine acts against the importation of diseased plants, have brought the subject home to every one.

The pioneer work by Professor H. H. Whetzel, of Cornell University, on the history of

phytopathology is therefore a timely and serviceable contribution. The subject is treated by Professor Whetzel in an attractive and perspicuous manner, and covers from the most ancient times to the present. Both the development of concepts regarding the nature and treatment of diseases as well as the dominating influence of phytopathological writers are taken into consideration in dividing the time into eras, and again into periods.

Scarcely thirty pages are given to the three incubation eras, called the Ancient, Dark and Premodern Eras, but they are most readable pages, and clearly point out the course of the early development of the subject.

The Modern Era, extending from 1853 to 1906, was one of great activity in all scientific lines. During this time phytopathology became a distinctive science. Many investigators of forceful personality and marked ability gave direction to the work of discovery, and in consequence the boundary of knowledge in the field of plant diseases was enormously extended. The center of pathological activity in its academic aspects was at first in Germany, and in its practical and commercial aspects in France, but in both aspects the foremost advance began to shift to America in the eighties, and soon this country became the leader in initiative as well as in the amount of investigation.

The present era, now just entering its second decade, has seen the establishment of chairs of phytopathology in many universities, the rise of the American Phytopathological Society and of the journal Phytopathology, the enactment of effective quarantine measures against the international and interstate movement of diseased plants, a new class of fungicides with sulphur in place of copper, the discovery of the canceroid nature of crown gall, and in general the recognition by men of affairs as well as by the cultivator of the vast importance of the utmost detailed information regarding plant diseases and of cooperative and efficient means for making such knowledge available in protecting all sorts of crops and plant life.

This orderly presentation of the evolution of

a science destined to play an increasingly wider and more important part in the affairs of human well-being and achievement is particularly timely. Professor Whetzel has compressed into the hundred and thirty pages of his book a well balanced and helpful outline of the historical aspects of the science. It is a valuable addition to botanical literature. J. C. ARTHUR

PURDUE UNIVERSITY

SPECIAL ARTICLES

RESISTANCE IN THE AMERICAN CHESTNUT TO THE BARK DISEASE

DURING the past summer, in connection with the Office of Forest Pathology, U. S. Department of Agriculture, the writer investigated conditions in the American chestnut looking toward immunity or disease resistance to the well-known bark disease. A thorough search was carried on, which, for obvious reasons, was restricted mainly to the immediate neighborhood of New York City. The results are deemed of sufficient importance to warrant publication here in advance of a more detailed account.

No immune trees were found, but a considerable number of resistant trees were located, some of them on the island of Manhattan itself. The following points are considered evidence of a resistant quality in these trees.

1. The result of inoculation tests. The average lateral growth of the fungus in 289 inoculations was 0.6 cm. for a period of from 5 to 6 weeks-mainly in August. This is about one fourth the figure (2.2 cm.) given by Anderson and Rankin for normal trees during the month of August at Napanoch, New York, and about one fifth the figure (2.83 cm.) given for the same month by the same investigators at Charter Oak, Pennsylvania.1

2. The occurrence of the trees in a neighborhood long subject to the disease, and the presence among the trees of individuals long since dead.

1 Anderson, P. J., and Rankin, W. H., "Endothia Canker of Chestnut," Cornell Univ. Agric. Expt. Sta. Bull. 347, pp. 574, 575, 1914.

3. Evidence of the long period the disease has been present in the trees themselves; i. e., bare, weathered tops; healed cankers; thrifty branches, with bases diseased and hypertrophied, but living, etc.

4. Peculiarities of the bark; such as extensive development of a callus tissue, and the presence of a peculiar substance which is constantly associated with, and particularly conspicuous in cases of marked resistance.

5. The natural grouping of the trees in welldefined areas or "pockets," pointing to a genetic variation.

6. The manifestation by members of the same coppice group; and by branches, trunk and basal shoots of the same individual; of similar degrees of resistance, indicating an inherent condition.

If these facts and inferences are correct, they point the way clearly toward a reconstruction and a revival of our American chestnut. Many of the trees bloomed well, and this fall bore good fruit. A large number of nuts have been gathered and planted by Dr. Van Fleet, of the U. S. Department of Agriculture, at the trail grounds near Washington, D. C. If the resulting seedlings substantiate the inference that the disease resistance is a heritable character, the way lies open, both by inbreeding, and by crossing with the resistant oriental species (not good timber trees themselves) to develop an extremely resistant or perhaps practically immune strain of timber tree for the reforestation of our devastated chestnut woodlands.

ARTHUR HAR MOUNT GRAVES OFFICE OF INVESTIGATIONS IN FOREST PATHOLOGY, BUREAU OF PLANT INDUSTRY, WASHINGTON, D. C.

THE OCCURRENCE OF AZOTOBACTER IN

CRANBERRY SOILS

SEVERAL papers have appeared recently in SCIENCE and elsewhere1, 2 concerning the fact that the aerobic non-symbiotic nitrogen fixing. organisms, namely the Azotobacter group, occur in the soil, when the concentration of the 1 Gainey, SCIENCE, Vol. 48, pp. 139-140, 1918; Jour. Agr. Res., Vol. 14, pp. 265-271, 1918.

2 Gillespie, SCIENCE, Vol. 48, pp. 393–394, 1918.

hydrogen-ion is not more than 10-6, or the limiting exponent is 6.0.

Investigators have gone so far as to use the presence of Azotobacter in the soil as an indication of the soil reaction. Gillespie, interpreting the results of Christensen," stated that they are in accord with those obtained by Gainey,1 namely the limiting hydrogen-ion exponent for the presence of Azotobacter in the soil is 6.0.

The methods previously used in determining the soil acidity conveyed only a very indefinite idea about the true nature of the reaction of the soil. But only recently 4,5 methods have been suggested which, either using the electrometric or an improved colorimetric method, have enabled us to get a better insight into the extent and nature of soil acidity. These studies have brought out the facts referred to above concerning the reaction limit for the existence of Azotobacter in the soil.

In the study of the microbial population of cranberry soils some interesting observations were made and of these only the occurence of Azotobacter will be reported here.

The cranberry soils are so distinctly different from ordinary soils that it was thought for a long time that no very large number of bacteria can exist in them and that the microbial population consists predominantly of molds. These soils are known to have a distinctly acid reaction and contain large quantities of undecomposed organic matter, namely the roots and the stubble of the dead plants. The existence of Azotobacter in cranberry soils would be of great practical importance, since the nitrogen of the air would thus be fixed and made available to the crops, which have to grow in soils rather poor in available nitrogenous constituents (particularly is this true of sandy bottom bogs). The undecomposed roots and stubble would supply the carbohydrates necessary for the activities of Azoto3 Christensen, Soil Science, Vol. 4, pp. 115-178, 1917.

4 Gillespie, Jour. Wash. Acad. Sci., Vol. 6, pp. 7-16, 1916.

5 Sharp and Hoagland, Jour. Agr. Res., Vol. 7, pp. 123-145, 1916.

bacter, particularly in the presence of cellulose decomposing organisms.

The high acidity of the cranberry soils would preclude the very idea of finding the Azobacter in these soils and the early students of this group of organisms were of the opinion that they can not live in acid media at all but the reaction has to be adjusted first to neutrality before the conditions are made favorable for their activities.

A Savannah bottom cranberry bog situated at Whitesbog, N. J., was used for this work. A part of the bog was limed three years ago and the crop was almost double of the corresponding plot, unlimed. Samples of the soil from the two plots were secured under sterile conditions and used for this study. The soil is nothing more than some white sand interwoven with decayed and living plant residues.

The hydrogen-ion concentration of the two soils was determined by means of the colorimetric method, using the phenol-sulfon-phthalein indicators suggested by Clark and Lubs.7 The method corresponds very closely with the electrometric determinations using the hydrogen electrode, as was shown by Gillespie.2 A definite amount of soil was shaken with double its weight of distilled water, then centrifuged; the supernatant clear liquid was syphoned off and used for the determination of the hydrogen-ion concentration. The unlimed soil had an hydrogen-ion concentration of pH=5.4 to 5.6 while for the limed soil pH was 6.2-6.4.

The two soils were added in 10-gram quantities to 100 cc.c. portions of a sterile faintly alkaline nitrogen-free mannite solution and incubated at 25°. The solution in the flasks containing the limed soils became turbid in four days and a pellicle characteristic of Azotobacter began to develop in some flasks. On microscopic examination the solution was found to contain an abundance of Azotobacter cells and Actinomyces filaments. The solution in all the flasks to which the unlimed soil was added remained clear as in the control, but has shown a profuse gas production. • Lipman, Ann. Rept. N. J. Agr. Exp. Sta., pp. 262-268, 1904.

7 Jour. Bact., Vol. 2, Nos. 1, 2, 3, 1917.

On microscopic examination no Azotobacter cells and no Actinomyces filaments were discovered.

The limiting reaction for the existence of Azotobacter in the soil, expressed in the hydrogen-ion concentration is thus found to fall between pH-5.4 to 5.6 and pH-6.2 to 6.4 and is probably nearer the latter. This will confirm the results of Gainey1 and Christensen3 that an hydrogen-ion concentration of the soil = pH-6.0 is the limiting reaction for the activities of Azotobacter in the soil.

The occurrence of Antinomyces filaments together with Azotobacter cells suggests a still more interesting and important possibility, association between these two groups of soil microorganisms. As will be soon shown elsewhere many Actinomyces decompose organic residues very rapidly. The association between these two groups of organisms, change of reaction, and the action of Actinomyces upon the nitrogen-fixation by Azotobacter is being studied at present in this laboratory.

The importance of Azotobacter in cranberry soils, which can be effected by changing the reaction of those soils, thus becomes apparent: these organisms, whether alone or in association with others, utilize the plant residues as a source of energy and this allows them to fix the atmospheric nitrogen and increase its supply in the soil, which goes towards an increased crop production.