MICROSCOPIC WORK ON THE STRUCTURE OF WOOD 211 



not has been clearly shown. A careful study of the structure of several 

 woods and the changes which are produced in drying and under mechanical 

 stresses was made at Yale laboratory by Mr. W. D. Brush under the writer's 

 direction. A statement of his results, fully illustrated by excellent photo- 

 microgi-aphs and drawings, appears in an unpublished Forest Service report. 



The Service has planned a comprehensive line of work of this kind which 

 is now under way at the new Madison Laboratory. (Other microscopic work 

 on the histology of wood, but from the botanical standpoint, with a view to 

 the identification of species, is also being carried on in Washington in the 

 section of Dendrology.) The principal purpose of this work is to bring the 

 two fields of knowledge mentioned before into relationship by making clear 

 to the artisan, engineer or user of wood, the (microscopic) anatomical 

 structure and differences in structure of various woods which underlie the 

 physical and mechanical properties, and differences, in the material he is 

 using and with which he is already familiar. New uses and reasons for not 

 using various woods will also naturally be suggested. 



To exhibit these facts, chief reliance will be placed upon photomicro- 

 graphs of the wood sections and elements themselves. These will be arranged 

 in a systematic and logical manner and will be shown at uniform magnifica- 

 tions so that the micrographs of all the different species will be directly com- 

 parable. The views will be supplemented by such descriptions and discussions 

 as will lend clearness to the subject. This discussion will be in non-technical 

 language so as to be intelligible to the persons for whom it should be chiefly 

 valuable. 



It is believed that this proposed publication will be unique in this respect. 

 Among all the works covering these fields, nothing has been found with this 

 specific purpose in view, and giving illustrations in a comprehensive manner 

 and of uniform style. It is our purpose, as far as possible, to make the illus- 

 trations speak for themselves, which will be in a universal language not re- 

 quiring translation. 



The equipment of the laboratory for this research is very complete. As 

 a foundation, a collection of important commercial woods is being made. The 

 specimens consist of short logs from normal commercial trees, the sylvical 

 conditions of the place of growth of each specimen being recorded. From these 

 specimens small pencils are cut while green and preserved in paraffin or for- 

 malin without being allowed to dry out. The pencils are taken at a point 

 about four feet above the root swelling and run from bark to center. Thus 

 a representative piece is obtained for the microscopic sections. In many cases 

 another piece is taken from the top of the same tree. Thus far about one 

 hundred species have been obtained. 



The first part of the work consists in the preparation of a complete col- 

 lection of permanent microscopic slides. The small pencils cut from the wood 

 specimens are treated in the usual manner for preparing microscopic slides, 

 sectioned on a special microtome, stained and mounted in balsam. As a rule 

 three samples are taken from each pencil, one from the sap wood, one from 

 the main portion of the heartwood, and another from near the center of the 

 tree. From these samples sections are made in three planes; transverse, radial 

 and tangential. 



The microscopic slides thus completed would be of little use to the public 

 for the purpose intended without the next step, namely, the photomicrographs. 

 A complete equipment for this work is installed at the laboratory, including 

 a dark room and all accessories. The apparatus for making the photographs 

 consists essentially of an arc light, a system of condensing lenses, ray filters 

 for obtaining monochromatic light, microscope and lenses, shutter, camera 



