100 FORESTRY INVESTIGATIONS U. S. DEPARTMENT OF AGRICULTURE. 



(9) Pits, simple and bordered, especially the number of simple pits in the cells of the pith 

 rays, which lead into each of the adjoining tracheids. 



For standards of weight, consult table on page 95; for standards of hardness, statement on 

 page 97. 



Unless otherwise stated the color refers always to the fresh cross section of a piece of dry 

 wood; sometimes distinct kinds of color, sometimes only shades, and often only general color 

 effects appear. 



HOW TO USE THtt KEY. 



Nobody need expect to be able to use successfully any key for the distinction of woods or of 

 any other class of natural objects without some practice. This is especially true with regard to 

 woods, which are apt to vary much, and when the key is based on such meager general data as 

 the present. The best course to adopt is to supply one's self with a small sample collection of 

 woods accurately named. Small, polished tablets are of little use for this purpose. The pieces 

 should be large enough, if possible, to include pith and bark, and of sullicient width to permit 

 ready inspection of the cross section. By examining these with the aid of the key, beginning 

 with the better-known woods, one will soon learn to see the features described and to form an idea 

 of the relative standards which the maker of the key had in mind. To aid in this, the accom- 

 panying illustrations will be of advantage. When the reader becomes familiar with the key, the 

 work of identifying any given piece will be comparatively easy. The material to be examined 

 must, of course, be suitably prepared. It should be moistened; all cuts should be made with a 

 very sharp knife or razor and be clean and smooth, for a bruised surface reveals but little struc- 

 ture. Tlie most useful cut may be made along one of the edges. Instructive, thin, small sections 

 may be made with a sharp penknife or razor, and when placed on a piece, of thin glass, moistened 

 and covered with another piece of glass, they may be examined by holding them toward the light. 



Finding, on examination with the magnifier, that it contains pores, we know it is not conifer- 

 ous or nonporous. Finding no pores collected in the spring- wood portion of the annual ring, but 

 all scattered (diffused) through the ring, we turn at once to the class of ll Diffuse- porous woods." 

 We now note the size and manner in which the pores are distributed through the ring. Finding 

 them very small and neither conspicuously grouped, nor larger nor more abundant in the spring 

 wood, we turn to the third group of this class. We now note the pith rays, and finding them 

 neither broad nor conspicuous, but difficult to distinguish, even with the magnifier, we at once 

 exclude the wood from the first two sections of this group and place it in the third, which is repre- 

 sented by only one kind, cottonwood. Finding the wood very soft, white, and on the longitudinal 

 section with a silky luster, we are further assured that our determination is correct. We may 

 now turn to the list of woods and obtain further information regarding the occurrence, qualities, 

 and uses of the wood. 



Sometimes our progress is not so easy; we may waver in what group or section to place the 

 wood before us. In such cases we may try each of the doubtful roads until we reach a point 

 where we find ourselves entirely wrong, and then return and take up another line; or we may 

 anticipate some of the later-mentioned features and finding them apply to our specimen, gain 

 additional assurance of the direction we ought to travel. Color will often help us to arrive at a 

 speedy decision. In many cases, especially with conifers, which are rather difficult to distinguish, 

 a knowledge of the locality from which the specimen comes is at once decisive. Thus, northern 

 white cedar, and bald cypress, and the cedar of the Pacific will be identified, even without the 

 somewhat indefinite criteria given in the key. 



KKY TO THE MORE IMPORTANT WOODS OF NORTH AMERICA. 



/. Nonporous woods. Pores not visible or conspicuous on cross suction, even with magnifier. Annual rings 

 distinct by denser (dark-colored) bands of summer wood (fig. 37). 



//. Ring-porou* woods. Pores numerous, usually visible on cross section without magnifier. Annual rings 

 distinct by a /one of large pores collected in the spring wood, alternating with the denser summer wood (tig. 5). 



///. Diffuse-porous iroodn. Pores numerous, usually not plainly visible on cross section without magnifier. 

 Annual rings distinct by a fine lino of denser summer- wood cells, often quite indistinct; pores scattered through 

 annual ring; no zone of collected pores in spring wood (fig. 6). 



NOTE. The above-described three groups are exogenous, i. c., they grow by adding annually wooil on their 

 circumference. A fourth group is formed by the endogenous woods, like yuccas and palms, which do not grow by 

 such additions. 



