WOOD OF BROAD-LEAVED TREES 



29 



resembles the pith-rays, especially in tangential longitudinal sec 

 tions ; but its walls are not elongated radially. 



As has been said, the wood of broad-leaved trees may contain 

 from three to five of these different elements. Vessels are always 

 present, but in some cases tracheids are absent. The wood of 

 Plane, Ash, and Citrus (Orange, Lemon, etc.), for example, con- 

 sists of vessels, woody fibre, thin-walled fibrous cells and wood- 

 parenchyma only. That of Holly, Hawthorn, and Pyrus (Apple, 

 Pear, Rowan, etc.) is made up of vessels, tracheids, and wood- 

 parenchyma : that of Maples, Elder, Ivy, Euonymus, etc. contains 

 also thick-walled fibrous cells. The wood of Berheris (Barberry) 



WP T 



Fig 25 —A piece of dicotyledonous wood, magnified about 100 times A transverse 

 section is shown atoove, with a pith-ray {Pi ) crossing the zone of autumn wood 

 (a) which forms the outer boundary of an annual nng In front is a radial longi- 

 tudinal section showing wood parenchyma (If/"), some large tracheae (T), and much 

 wood fibre, crossed by another pith ray. The tangential section is m shadow. 



consists exclusively of vessels, tracheids, and thin and thick- 

 walled fibrous cells ; and that of Oaks, Hornbeams, Plum, and 

 Buckthorn of vessels, tracheids, woody fibre, and wood-paren- 

 chyma (Kgs. 25 and 26). The most common type of structure, how- 

 ever, occurring in Willows, Poplars, Alder, Birch, Walnut, Linden, 

 Magnolia^ Ailanthus, Bobinia, etc., contains vessels, tracheids, 

 woody fibre, thin-walled fibrous cells, and wood-parenchyma. 



The distinctive features of woods, however, depend rather 

 upon the proportions in which these elements are present, and 

 upon their arrangement, than upon the absence of any of the six 

 kinds of elements. There is, as a rule, among the woods of 



