146 



VEGETABLE FABRIC. 



[lesson 24 



large tubes, comparatively ; these are called Ducts, or sometimes 

 Wood almost always consists of both woody fibres and ducts, 

 variously intermingled, and combined 

 into bundles or threads which run 

 lengthwise through the root and stem, 

 and are spread out to form the frame- 

 work of the leaves (136). In trees 

 and shrubs they are so numerous and 

 crowded together, that they make a 

 ' solid mass of wood. In herbs they 

 are fewer, and often scattered. That 

 is all the difference. 



407. The porosity of some kinds of 

 wood, which is to be seen by the naked 

 eye, as in mahogany and Oak-wood, is 

 owing to a large sort of ducts. These 

 generally contain air, except in very 

 ' young parts, and in the spring of the 

 year, when they are often gorged with 

 sap, as we see in a wounded Grape- 

 vine, or in the trunk of a Sugar- Maple 

 at that time. But in woody plants 

 through the season, the sap is usually 

 carried up from the roots to the leaves 

 by the 



408. Wood-Cells, or Woody Fibre. (Fig. 342-345.) These are 

 small tubes, commonly between one and two thousandths, but in 

 Pine-wood sometimes two or three hundredths, of an inch in diam- 

 eter. Those from the tough bark of the Basswood, shown in Fig. 

 342, are only the fifteen-hundredth of an inch wide. Those of But- 

 ton wood (Fig. 345) are larger, and are here highly magnified be- 

 sides. They also show the way wood-cells are commonly put to- 

 gether, namely, with their tapering ends overlapping each other, — 

 spliced together, as it were, — thus giving more strength and tough- 

 ness to the stem, &c. 



FIG. 342. Two woort-cells from tlio inner or fibrovia bark of the Linden or Bnpswood. 

 343. Some tissue of tlie wood of tile same, viz. W"od-ceiIs, and below (rf) a portion of a 

 Bpirally marked duct 344. A separate wood-cell. All equally magnified. 



FIG. 345. Some wood-cells of . Biittonwood, higbly magnified ; a, thin spots in the 

 walls, looking like holes; on the right-hand Bide, where the walls are cut through, these 

 ih) are seen in jirufile. 



