390 FORESTRY INVESTIGATIONS U. S. DEPARTMENT OF AGRICULTURE. 



summer wood are marked on paper with the aid of the camera, and thus a panorama of the entire 

 section is brought before the eye. The histology of the wood, the resin ducts, the tracheids and 

 medullary rays, their form and dimensions, are studied in thin sections magnified 580 diameters 

 and even more. Any peculiarity in form or arrangement is drawn with the camera and thus 

 graphically recorded; the dimensions are measured in tlic manner described for the measurement 

 of the summer wood, or with the ocular micrometer. In measuring cell walls the entire distance 

 between two neighboring lamina is taken as a "double wall," the thickness of the wall of either of 

 the two cells being one-half of this. The advantage of this way of measuring is apparent, since 

 the two points to be marked are in all cases perfectly clear and no arbitrary positions involved. 

 The length of the cells is found in the usual way by separating the elements with Schultxc's 

 solution (nitric acid, chlorate of potassium). All results tabulated are averages of not less than 

 ten, often of more than one hundred, measurements. 



In the attempt to find the quantitative relations of the different tissues, as well as the density 

 of each tissue, various ways have been followed. In some cases drawings of magnified sections 

 were made on good, even paper, the different parts cut out, and the paper weighed. In other cases 

 numerous measurements and computations were resorted to. Though none of the results of these 

 attempts can be regarded as perfectly reliable, they have done much to point out the relative 

 importance of different constituents of the wood structure, and also the possibility and practica- 

 bility, and even the necessity, of this line of investigation. 



INSTRUCTIONS AND BLANK FORMS, WITH ILLUSTRATIVE RECORDS. 

 INSTRUCTIONS FOR THE COLLECTION OF TEST PIECES OF PINKS FOR TIMBER INVESTIOATIONS. 



A. OBJECT OF WORK. 



The collector should understand that the ultimate object of these investigations is, if possible, to establish the 

 relation of quality of timber to the conditions under which it is grown. To accomplish this object he is expected 

 to furnish a very careful description of the conditions under which the test trees have grown, from which test pieces 

 are taken, ('are in ascertaining these and minuteness and accuracy of description are all-important in assuring 

 proper results. It is also necessary to select and prepare the test pieces exactly as described and to make the records 

 perfect as nearly as possible, since the history of the material is of as much importance as the determination in the 

 laboratory. 



IS. LOCALITIES FOR COLLECTING. 



As to the locality from which test trees are to be taken, a distinction is made into station and site. 



By station is to be understood a section of country (or any places within that section) which is characterized 

 in a general way by similar climatic conditions and geological formation. "Station," then, refers to the general 

 geographical situation. "Site" refers to the local conditions and surroundings within the station from which test 

 trees are selected. 



For example, the drift deposits of the Gulf Coast plain may be taken for one station; the limestone country of 

 northern Alabama for a second. But a limestone formation in West Virginia, which differs climatically, would 

 necessitate another station. Within the first station a rich, moist hummock may furnish one site, a sandy piece of 

 upland another, and a wet savannah a third. Within the second or third station a valley might furnish one site, 

 the top of a hill another, a different exposure may call for a third, a drift-capped ledge with deeper soil may warrant 

 the selection of another. 



Choice of stations. For each species a special selection of stations from which test pieces are to be collected is 

 necessary. These will be determined, in each case separately as to number and location, from this office. It is 

 proposed to cover the field of geographical distribution of a given species in such a manner as to take iu stations 

 of climatic difference and different geological horizon, neglecting, however, for the present, stations from extreme 

 limits of distribution. Another factor which will determine choice is character of soil, as dependent upon geological 

 formations. Stations which promise a variety of sites will be preferably chosen. 



Choice of site. Such sites will be chosen at each station as are usually occupied by the species at any one of 

 the stations. If nnnsnal sites are found occupied by the species at any one of the stations it will be determined by 

 special correspondence whether test pieces are to be collected from it. The determination of the number of sites at 

 each station must be left to the judgment of the collector after inspection of the localities; but before determining 

 the number of sites the reasons for their selection must be reported to this office. The sites are characterized and 

 selected by differences of elevation, exposure, soil conditions, and forest conditions. The difference of elevation 

 which may distinguish a site is provisionally set at 500 feet; that is, with elevation as the criterion for choice of 

 stations the difference must be at least 500 feet. Where differences of exposure occur a site should be chosen ou 

 each of the exposures present, keeping as much as possible at the same elevation and under other similar conditions. 

 Soil conditions may vary in a number of directions, in mineral composition, physical properties, depth, and nature 

 of the subsoil. For the present, only extreme differences in depth or in moisture conditions (drainage) and decided 

 difference in mineral composition will be considered in making selection of sites. 



