146 



A'EGETABLE FABRIC. 



[lesson 24. 



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

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

 342 343 345 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 (13G). 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. Tlie 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 

 }'ear, when they are often gorged with 

 sap, as we see in a wounded Grape- 

 vine, or in tlie trunk of a Sugar-Maple 

 at that time. But in woody ])lants 

 through the season, tlie sap is usually 

 carried up from the roots to the leaves 

 by the 



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

 email 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. 

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

 tonwood (Fig. 345) are larger, and are here higlily 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. 



Fro. .?42. Two wood-cells from tlie inner or fibrous bark of the Linden or Basswood. 

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

 spirally marked duct. 3-44. A separate wood-cell. All equally magnified. 



FIG. 345. Some wood-cells of Buttonwood, liifrhly niagniliod : a, lliin spots in the 

 walls, looking like Jioles ; on the right-hand side, where the walls are cut tlirough, thes« 

 i^b) are seen in prufilq. 



