III.] THE CLASSIFICATION OF TIMBERS, 47 



The false zones of soft tissue are often seen to run 

 into one another, whereas this is not the case with true 

 rings, however excentric they are. 



The next character of general importance is the 

 presence or absence of vessels — often called " pores " 

 by technologists — as seen on the transverse section ; 

 and there are certain peculiarities connected with 

 them. 



The first thing to note is a possible danger of the 

 tyro mistaking the resin-canals of Conifers for these 

 vessels of the wood : practical aquaintance with the 

 irregular outline and very different structure and 

 distribution of these canals will alone serve the 

 student here. Vessels (excluding the small spiral 

 vessels of the proto-xylem which form the so-called 

 " medullary-sheath," and which do not come into con- 

 sideration) are found in the wood of all Dicotyledons, 

 except Drimys and one or two of its allies, while they 

 are as regularly absent from that of the Conifers ; 

 consequently it is easy at the outset to distinguish 

 the woods of these two great groups at a glance, at 

 least with the aid of a lens. In the Dicotyledons, 

 however, considerable differences are to be observed 

 regarding the vessels ; and first, as to their size. 



The rule Is that the vessels are largest and most 

 numerous in the spring-wood, diminishing outwards 



