INTRODUCTION. 25 



various other vessels occur in the wood, and their 

 number, mode of grouping, width of calibre, and the 

 thickness and markings of their walls afford valuable 

 characters in recognising timbers. 



Thus the vessels are much more numerous in the 

 Willows, Poplars, Lime, etc., than on an equal area of 

 Ash, Oak, or Walnut. They differ much in size, also, 

 being large enough to see without a lens in Vines, 

 AristolocJiia, and even in Oaks and Palms, etc., whereas 

 they are so small in Box, Willows, Birch, etc., that the 

 beginner is apt to confound these woods with that of 

 Conifersj which have no vessels. 



Then, again, many woods examined in transverse 

 section have the vessels grouped in clusters, beautifully 

 seen in the Buckthorn and Elms, whereas others — e.g. 

 Beech — have them equably distributed. Moreover, the 

 grouping may be different in different parts of the 

 transverse section, large vessels in one region and 

 smaller ones elsewhere, e.g. Oak, Ash, etc., and many 

 other peculiarities are noticeable, especially in the 

 microscopic characters of the vessels themselves. 



Cells always occur in the medullary rays, but they 

 are often either very sparse or absent in the wood 

 proper, whereas in some woods — e.g. Ailanthus, 

 Erythrina, Bombax, etc, — they are so abundant as to 

 give the timber a peculiarly soft and pith-like character. 

 In many timbers, also, these cells are arranged in a 

 definite manner, giving contrast-markings on the 

 transverse sections as seen by the unaided eye : such are 

 well seen in species of Ficus, and many Leguminosae. 

 Possibly no wood is totally devoid of cells, but in very 

 many they are confined to the neighbourhood of 

 the vessels and medullary rays, and are so few in 

 number that their presence is doubtful. 



