(2) The summer wood is also distinguishable by the fact that, as with the conifers, its cells are smaller and its cell walls thicker than those of the spring wood. The summer wood appears only as a narrow, dark line along the largest pores in each ring. (3) The lines of the pith rays are very plain in some woods, as in oak. No. 47, Chap. III. (4) The irregular arrangement and (5) Complex structure are evident, and these are due to the fact that the wood substance consists of a number of different elements and not one (tracheids) as in the conifers. Looking at the radial section, Fig. 20: (6) If the piece is oak, the great size of the medullary rays is most noticeable. Fig. 32, p. 38. They are often an inch or more wide; that is, high, as they grow in the tree. In ash they are plain, seen thru the microscope, but are not prominent. (7) The interweaving of the different fibers and the variety of their forms show the structure as being very complex. In the tangential section, Fig. 20: (8) The pattern of the grain is seen to be marked not so much by the denseness of the summer wood as by the presence of the vessels (pores). (9) The ends of the pith rays are also clear. In _diffuse porous woods_, the main features to be noticed are: In the transverse section, Fig. 21: (1) The irregularity with which the pores are scattered, (2) The fine line of dense cells which mark the end of the year's growth, (3) The radiating pith rays, (4) The irregular arrangement and, (5) The complex structure. In the radial section, Fig. 21: (6) The pith rays are evident. In sycamore, No. 53, Chap. III, they are quite large. (7) The interweaving of the fibers is to be noted and also their variety. In the tangential section, Fig. 21: (8) The grain is to be traced only dimly, but the fibers are seen to run in waves around the pith rays. (9) The pith rays, the ends of which are plainly visible. [Illustration: Fig. 21.] THE GRAIN OF WOOD. The term "grain" is used in a variety of meanings which is likely to cause confusion. This confusion may be avoided, at least in part, by distinguishing between grain and texture, using the word grain to refer to the arrangement or direction of the wood elements, and the word texture to refer to their size or quality, so far as these affect the structural character of the wood. Hence such qualifying adjectives as coarse and fine, even and uneven, straight and cross, including spiral, twisted, wavy, curly, mottled, bird's-eye, gnarly, etc., may all be applied to grain to give it definite meaning, while to texture the proper modifying adjectives are coarse and fine, even and uneven.