The interchange of plants and seeds with other horticultural and botanical establishments has been continued during the year. Including grafts and cuttings, 6428 plants, and 1240 packets of seeds have been distributed as follows: To the United States, 6418 plants and 882 packets of seeds; to Great Britain, 10 plants and 309 packets of seeds; to France, 18 packets of seeds; to Egypt, 2 packets of seeds; to New Zealand, 1 packet of seeds; to Japan, There have been received 1266 plants and 179 packets of seeds as follows: From the United States, 1256 plants and 98 packets of seeds; from Great Britain, 10 plants; from Korea, 81 packets of seeds.

28 packets of seeds.

The usual instruction in dendrology has been given in the Arboretum by Assistant Professor J. G. Jack, who from May to June held weekly field meetings attended by sixteen students, principally teachers. Three special students have used the facilities of the Arboretum continuously through the year.

In June the fifth and final volume of the Bradley Bibliography was published. This work, which was commenced in 1900, contains the titles of books and of articles in the Proceedings of Scientific Societies and Journals relating to the woody plants of the world, in all languages, published before the beginning of the twentieth century. The five quarto volumes contain 3895 doublecolumn pages and rather more than 100,000 titles. It was intended that this book should be paid for by the income of the fund given to the Arboretum by Miss A. A. Bradley in memory of her father, William L. Bradley, a man devoted to agriculture and interested in planting trees. The cost, however, of preparing and printing it has far exceeded the income of the fund and the annual contributions made by Miss Bradley to increase it; and this deficit has been provided for out of gifts made by other friends to the Arboretum to increase its income.

Without the interest and generosity of the members of the Committee appointed by the Overseers to visit the Arboretum, and of many other friends of the institution, it would have been impossible to have maintained this Department of the University and to have carried on its scientific activities; and I take this opportunity to express to them my thanks for the opportunities which they have given me to make the Arboretum an important dendrological station.

C. S. SARGENT, Director.

TO THE PRESIDENT OF THE UNIVERSITY:

SIR, The enrolment in the courses in Chemistry during the past year was a third less, and the number of research students twothirds less, than last year. The missing graduate and advanced students in Chemistry will, however, almost all be found at work in the various branches of the Chemical Warfare Service of the U. S. Army.

The teaching staff has been depleted in much the same way. Professor Kohler, Assistant Professors Lamb and Jones and Dr. Conant have been on leave of absence engaged in war work. Professor Kohler has been in charge of Offense Problems; Assistant Professor Lamb, Chief of the Defense Section, Chemical Research; Dr. Conant, Chief of a Unit in the Offense Section, Chemical Research; all in the Research Division of the Chemical Warfare Service. Professor Jones has been acting as Consulting Chemist for the United States Tariff Commission at Washington.

The investigations carried on by the members of the Division not on leave have been as follows:

Professor Michael continued his study on the relation of ring formation to the length of chain in organic compounds.

Professor Richards, in collaboration with several assistants and students, carried out the following investigations:

With Dr. W. C. Schumb he studied the refractive indices and solubilities of ordinary lead nitrate and that from radioactive sources, finding the two refractive indices and the two molar solubilities to be respectively identical, and thus adding to our knowledge of the extraordinary anomaly involved. With W. M. Craig he investigated the purification of the rare element gallium through the sublimation of its trichloride, and with Dr. J. Sameshima determined the atomic weight (70.1) of the metal in this purified compound. S. Boyer assisted him in purifying gallium electrolytically and in determining the compressibility and density of this metal, both in the solid and the liquid conditions - data of significance in comparing the fundamental properties of the elements. Preliminary notes on all these investigations are in press.

Professor Richards also carried on important chemical work of a confidential nature for the War Department and the Department of Justice.

Professor Baxter, in collaboration with Mr. C. H. Wilson, continued experiments on the electrolytic method of determining cadmium, zinc and tin by deposition in a mercury cathode. With Professor M. Kobayashi he investigated further the determination of potassium as perchlorate, and commenced a redetermination of the atomic weight of mercury by electrolysis of the dichloride with a mercury cathode. With P. F. Weatherill he determined the change in volume during solution in water of potassium chloride at a number of temperatures where evidence was lacking. Grants from the Bache fund and the Gibbs fund of the National Academy were of assistance in his work.

Professor Baxter also carried out, with the assistance of Corporal C. H. Wilson, C.W.S., U.S.A., who was detailed back to Cambridge for that purpose, a number of investigations for the Research Division of the Chemical Warfare Service.

Professor Henderson, in collaboration with the Division of Food and Nutrition of the Medical Department of the U. S. Army, studied the physical chemistry of bread and bread making. He was assisted by Lieutenants E. J. Cohn, P. H. Cathcart, W. O. Fenn, and J. D. Wachmann. During the summer Professor G. Burrows of the University of Vermont greatly aided the work as a volunteer. Professor Wolbach of the Harvard Medical School also very kindly collaborated in the bacteriological study of ropy bread. The subjects studied included the acid-base equilibrium of the proteins, glutenin and gliadin, of gluten and of dough, and the action of electrolytes upon these substances; the physical properties of gluten and of dough; the conditions governing the fermentation and rise of dough; the baking of bread; the conditions which lead to the development of ropy bread; and the use of serum as a substitute for gluten in bread making. At the request of the Food Administration a few experiments were also made upon the importance of sugar in bread making, and, in coöperation with the Food Administration and a committee of bakers, instructions regarding methods of combating ropy bread were published. In collaboration with the Bureau of Chemistry of the Department of Agriculture observations were made on the effect of bleaching upon the properties of flour.

Dr. Hill after Professor Kohler's departure assumed direction of a number of problems then under way. They were as follows:

With W. G. O. Christiansen, the chlorination of dimethyl sulphate; the preparation of ethylene chlorhydrine; the oxidation of 2.4 dinitro toluene; the catalytic oxidation of ethyl alcohol to acetic acid. With J. B. Abrams and J. N. Aronson, the preparation of para dimethyl amino benzaldehyde.

Professor Richards received another grant of $2700 from the Carnegie Institution of Washington for a continuance of his work.

ARTHUR B. LAMB, Director.

TO THE PRESIDENT OF THE UNIVERSITY:

SIR, During the past year the regular teaching work of the Department of Physics, in its higher regions, was seriously restricted by the absence of Professors Pierce, Lyman, Davis, and Bridgman, but most of the courses in the lower and middle groups were vigorously maintained in spite of the fact that several of the assistants and instructors were called away for Government service during the year. Research work was very greatly reduced, being limited almost entirely to investigations in Sound, carried on by one or two undergraduates under the direction of Professor Sabine, two researches in photoelectric fields by one Chinese student and one Japanese student working under Professor Duane, and a study of the latent heat of vaporization of gasoline made by Dr. Blackwell for the Government service. In addition, the facilities of the Laboratory were used for purposes of investigation by two or three officers sent here by the Government to study a certain problem relating to poisonous gases.

This year also it has seemed advisable, as it did last year, to postpone the usual binding of the recently printed "Contributions," although sufficient material for a good sized volume is now on hand. It is to be hoped that next year the practice of issuing our" Contributions" in collected form will be resumed.

The Friday Conferences on topics of special interest to physicists, which had been maintained with so much profit to the Department during the years 1915-16, 1916-17, were discontinued during the past year, but the weekly Colloquium was maintained.

EDWIN H. HALL, Acting Director.