146 



VEGETABLE FABRIC. 



[LESSON 24. 



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



Vessels. Wood almost always consists of both woody fibres and ducts, 



3^2 343 s 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 

 1 solid mass of wood. In herbs they 

 are fewer, and often scattered. That 

 is all the difference. 

 4 407. 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 

 6 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-w r ood 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 wood-cells from the inner or fibrous bark of the Linden or Baspwood. 



343. Some tissue of the wood of the same, viz. wood-cells, and below (</) a portion of a 

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



FIG. 345. Some wood-cells of Buttonwood, highly magnified : a, thin spots in the 

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

 (i) are seen in profile. 



