WOODS AND THEIR DESTRUCTIVE FUNGI 435 



more highly differentiated than that of the conifers ; beside the wood- 

 cells, there are ducts, vessels, and special cells containing starch in the 

 alburnum or sap-wood. In nearly all the species of the first five 

 orders mentioned, the ducts grow in concentric rows, in the first of 

 the season's growth ; those which, form later may be inclined through 

 the layer of wood-cells, becoming smaller as they approach the outer 

 portion. In the live oak, the ducts run radially through the ring, 

 and the small fibers are nearly solid, giving the wood great hardness, 

 making it so valuable for ship-building. 



In the maples, beeches, birches, and magnolias the ducts are well 

 interspersed through the entire ring, and are nearly of the same size. 

 In the alburnum of these woods there are a great many cells which 

 are filled with starch as reserve material, like the medullary rays in this 

 portion of the wood. During active growth the starch is transformed 

 and withdrawn. In the duramen but little starch remains, other prod- 

 ucts taking its place. 



In the hard woods, all or portions of the annular rings are made 

 up of hard and nearly solid fibers, while in the softer woods the walls 

 are not so thick. In many of the species each layer of growth is not 



Fig. 3. Transverse Section of Quercus 



20 



alba,^ 



Fia. 4. Transverse Section of Liriodendron 

 talipfera, ^ (White Wood). 



of uniform thickness or quality, some having but comparatively few 

 of the dense, hard fibers, the growth of these depending upon certain 

 climatic conditions which may not yearly occur. 



In the thick forests, under quite uniform conditions of growth, the 

 thickness of the annular ring largely depends upon the leaf-area, 

 which remaining practically the same in the older trees, the wood-cells 

 forming upon a larger diameter, the rings as a rule are not so thick 

 or dense as those grown when the tree is much younger. 



Formerly, in lumbering, the trees were felled in the winter, cut 

 into logs, sledded on the snow to the streams, and driven down in rafts 

 in the spring to the mills. Now, with the log-railroads, they are in- 

 dependent of the snow, and in many camps lumbering is carried on 



