ANATOMICAL STRUCTURE. 265 



tion, &c., in spring), and their number and size affect the 

 technical properties of timber. In Conifers they are narrow 

 and close, giving a sort of silky gloss to a thin transverse 

 section ; but in broad - leaved trees they are usually more 

 prominent, being largest of all in Oak, where they form the 

 " flowering " when planks are cut radially to show " the silver 

 side." The medullary rays are broadest in Oak and Beech, 

 and highest in Oak and Alder ; fairly broad in Ash, Elm, 

 Maple, Sycamore, Plane, and Hornbeam ; narrow in Alder, . 

 Birch, Cherry, Chestnut, Horse-Chestnut, Lime, and Eobinia; 

 and almost indistinguishable in Willows and Poplars. The 

 wood of Conifers differs further from that of broad-leaved trees 

 by usually having resin-ducts or tubular spaces surrounded by 

 resin - producing cells without definitely constructed walls. 

 These resin-ducts are not only found running longitudinally in 

 the stem and branches, usually in the summer zone of wood, 

 but also occur along the medullary rays. Both of these two 

 kinds of resin-ducts communicate with each other, and the total 

 quantity of resin stored up in the wood has a great influence on 

 its technical properties. 



The width of each annual ring of wood varies with the soil 

 and situation, and with the amount and intensity of light 

 during the growing-period ; and the annual rings are usually 

 broader in young and middle-aged than in old trees, while they 

 are always broadest near the butt of the stem ; but the best 

 class of timber is that in which the breadth of the successive 

 annual rings is fairly equal, and where the annual rings have 

 a relatively broad dense zone of summer wood formed during 

 the warmest time of the year. 



In Conifers the annual rings are usually very distinct, and 

 also in Oak, Ash, Elm, and Chestnut ; but in Beech, Horn- 

 beam, Maple and Sycamore, Lime, Willow, Poplar, and Birch, 

 there is little difference between the Spring and the Autumn 

 zone in each annual ring. 



