PETIOLES OF THE COTTONWOOD.—The leaves of the Cottonwood as well as some other species of Populus have an interesting light relation. If one looks at a vigorous shoot, the leaves are seen to be arranged in the profile position around the stem. This is accomplished by means of a very simple device. The petiole is much flattened next to the blade and is quite flexible. The flattening is transverse to the plane of the blade and on this account the leaf will assume the vertical position, no difference in what way it is attached or twisted. This adaptation is also responsible for the musical rustle one hears when resting in the shade of the Cottonwood. The leaves are very smooth and nearly alike on both sides. Because of these and other adaptations, the Cottonwood is one of the most successful of our semi-xerophytic trees and one of the last stragglers to be found in the western part of the great plains. J. H. S. Ohio State University Six distinct and independent Colleges, each with a Dean and Faculty of its own. THIRTY SEVEN DEPARTMENTS. THIRTY DISTINCT COURSES. AGRICULTURE, ARTS, LAW, ENGINEERING, PHARMACY, VETERINARY MEDICINE. Superior facilities for education in Applied Science. Short or special courses for mature students not candidates for degrees. One hundred and twenty one instructors. Over thirteen hundred students. FINEST GYMNASIUM IN THE WEST. _For further information address the President_, DR. W. O. THOMPSON, STATE UNIVERSITY, COLUMBUS. Ohio Forest Trees Identified by Leaves and Fruit. By W. A. KELLERMAN, PH. D., Ohio State University. A neat pamphlet for every one who wishes to learn our native forest trees. Keys simple. Description plain. Can learn the names of the trees easily. Price reduced from 25 cents to 10 cents. Also, =The Fourth State Catalogue of Ohio Plants=. Bound copies at cost of binding, namely 20 cents. Gives list of scientific and common names; distribution by counties. Teachers and others will also be interested in Prof. Kellerman’s Phyto-theca or Herbarium Portfolio, _Practical Studies_ in Elementary Botany, _Elementary Botany_ with Spring Flora, all published by Eldredge & Bro., Philadelphia, to whom apply. For information or copies of _Forest Trees_ and _Catalogue_ or names of plant specimens of your region _address_ W. A. KELLERMAN, COLUMBUS, OHIO American Entomological Co. 1040 DE KALB AVENUE, BROOKLYN, N. Y. Lepidoptera Price List No. 2.—_Price 5 cents_ Refunded to Buyers ISSUED NOVEMBER 15th 1900. Dealers of all kinds of _ENTOMOLOGICAL SUPPLIES_ Manufacturers of the Original and Celebrated SCHMITT INSECT BOXES. _Builders of INSECT CABINETS, ETC._ The Twentieth Century Text Books of Biology.