MINUTE CHARACTERS. 11 



vessel of the wood of Cariniana is shown in fig. 3, with which compare 

 the segment- of a vessel from the wood of true mahogany, fig. 9, a.) 



Vessels are seen to best advantage in longitudinal sections (figs. 6, a, 

 and 11, a); individually the segments of which the vessels are com- 

 posed are from 1 to 2, or occasionally from 3 to 4, times as long as 

 wide, and as a rule their end walls are finally wholly absorbed (fig. 3, c). 

 These end walls are occasionally at right angles to the vessel, but they 

 are more often slanting surfaces always facing the pith rays. The 

 side wails have small, round, or elliptical, bordered pits, 1 arranged in 

 numerous perpendicular rows (fig. 3, d). The pits in the vessel walls 

 of Swietenia mahagom are usually smaller and are arranged more or 

 less in groups (fig. 9, d). » 



Wood fibers (fig. 6, h) are arranged in several or many radial rows 

 between the pith rays (fig. 6, d) and form the principal bulk of the 

 wood. (Contrast the arrangement of these fibers with that of those 

 of true mahogany, fig- 11, &.) Broad tangential bands of these ele- 

 ments alternate with obscure narrow lines of wood-parenchyma fibers 

 (fig. 6, c), which are clearly shown in both the transverse and radial 

 sections, when magnified 20 times the natural size. Wood fibers 

 having rather thick walls (fig. 4, b) and relatively small cavities are 

 seldom flattened, even in the region of vessels, which is true also of 

 most other woods with conspicuous pores. Wood fibers vary in 

 length from 0.97 to 1.6 millimeters, with an average of 1.29 milli- 

 meters, while the average width is about 0.02 millimeter. The pits 

 in the radial walls of wood fibers are simple * and slitlike (fig. 4, a). 

 A characteristic of true mahogany wood fiber is that it possesses cross 

 partitions (fig. 10, a) in striking contrast to the wood fiber of Carini- 

 ana. in which there are no cross partitions (fig. 4). 



Wood-parenchyma fibers (fig. 5) form very narrow bands which are 

 arranged at right angles to the pith rays (fig. 6, c). These bands are 

 usually 1, occasionally 2, and rarely 3 cells wide, and are visible 

 with a pocket lens magnifying from six to eight times natural size. 

 The wood is traversed by these very fine, light-colored, wavy bands, 

 which sometimes join one another or end abruptly when they meet a 

 pore, or in their undulating course are bent around the pores. These 

 narrow lines, not to be confounded with annual rings of growth, are 

 about as numerous as the pith rays themselves, and with them form 

 a meshlike structure. In true mahogany the wood-parenchyma 

 fibers for the most part surround the vessels and pith rays (fig. 11, c). 



x Pits are unthickened portions in the walls of wood elements. These are either round, elliptical, or slit- 

 like, and are further divided into simple and bordered pits. Whether a pit is simple or 

 mrri bordered is determined by the character of the canals which extend from the middle 

 u IjJ lamella, or common wall of two adjacent elements, to the cavity of the cell. When a 

 | transverse or longitudinal section is made, a profile view of pits will be seen, and if the 

 a ™~ walls of the canal are nearly parallel or diverge only slightly toward the common wall, as 

 is shown in fig. a, it is a simple pit. If the walls of the canal make a distinct angle just 

 Inside the pit opening, as shown in fig. 6, it is a bordered pit. 



